Ocular Prosthesis with Display Device

ABSTRACT

An ocular prosthesis includes a display device visible at an anterior portion of the ocular prosthesis. The display device is configured to present a changeable image that represents a natural appearance and movement for a visible portion of an eyeball of a subject. A system includes, besides the ocular prosthesis, an implant marker configured to move with an orbital implant disposed in an eye socket of a subject. A method includes determining a change in orientation of an orbital implant in a subject and determining an update to a natural appearance for a visible portion of an eyeball for the subject based on the change in orientation of the orbital implant. The method also includes rendering an update to an image of the natural appearance for a display device disposed in an ocular prosthesis configured to be inserted in the subject anterior to the orbital implant.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims benefit of Provisional Appln. 61/750,421, filedJan. 9, 2013, under 35 U.S.C. §119(e).

BACKGROUND OF THE INVENTION

Twelve thousand patients a year lose an eye in the U.S. from accidents,infections, cancer, congenital anomalies and advanced ocular conditionssuch as diabetes and glaucoma. It is estimated that a quarter of amillion Americans already have prostheses, and millions are estimated tohave such prostheses or are in need of such prostheses worldwide. Anocular prosthesis is generally a molded, painted methylmethacrylatedevice placed between the lids for people who have lost eyes. Thisplastic needs polishing and ultimately replacement about every fiveyears. Conventional prostheses may have a colored outer surface thatresembles the natural eye of the patient. Current prosthetic eyes canhave a good appearance in photographs, but have limited or no movementand therefore do not appear realistic when the patient attempts to movehis or her eyes. Also, conventional prostheses do not have pupils thatrespond to light. Therefore, such prostheses are a daily reminder of anobvious deformity and lead to insecurity of the patient, a reluctance tobe seen in public, a feeling of inferiority, and unhappiness.

Over the years ophthalmic surgeons have tried many ways to create aprosthesis that moves, but such attempts have failed. When the eye isremoved, a sphere (also referred to as an orbital implant) the size ofthe normal eye is placed in the socket and the conjunctiva (transparentmucous membrane that normally covers the sclera that is often referredto as the white portion of the eye) is surgically closed over thesphere. With modern surgical techniques, movement of the sphere is goodas the normal muscles around the eye (six of them) are often attached tothe sphere, either directly or indirectly by way of the conjunctiva. Theconjunctiva that is placed over the sphere, however, continues as thebulbar conjunctiva into the fornices above and below an anterior portionof the sphere, and continues as the palpebral conjunctiva that lines theundersurface of the upper and lower eyelids. The modern-day plasticprosthesis then sits within this closed loop of tissue (called theprosthesis space, hereinafter) formed by the palpebral conjunctiva, thebulbar conjunctiva and the conjunctiva. Many attempts to couple the balland the prosthesis have been tried since the first ocular prosthesis wascreated just over 100 years ago; however, it is believed that all suchattempts have failed to produce natural movement of the prosthesis.

SUMMARY OF THE INVENTION

The inventors have determined that one reason that such prostheses havefailed to achieve natural looking movement is for a simple anatomicreason—despite occasionally complete movement of the orbital implant,there is no space in the closed loop of tissue formed by the conjunctiva(called the prosthesis space, herein) for the prosthesis to movesufficiently to demonstrate normal motility. Techniques are provided forproviding realistic-looking movement in this confined prosthesis spaceusing a display device, such as an electronic or mechanical displaydevice. Thus, the inventors have developed a prosthetic eye that fits anunmet need for patients who have lost an eye to disease or trauma orcongenital malformations or cancer or severe infection, by providing aprosthetic eye that appears to have lifelike movements and, in someembodiments, a pupil that responds to light.

In a first set of embodiments, an ocular prosthesis includes a displaydevice visible at an anterior portion of the ocular prosthesis, whereinthe display device is configured to present a changeable image thatrepresents a natural appearance and movement for a visible portion of aneyeball of a subject.

In a second set of embodiments, an ocular prosthesis includes a housinghaving a form factor shaped to fit under an eyelid of a subject and infront of an orbital implant disposed in an eye socket of the subject,wherein an anterior portion of the form factor is curved similar to ananterior portion of a natural eyeball for the subject. The prosthesisalso includes a display device disposed within the housing and visibleat an anterior portion of the housing, and an implant detector disposedwithin the housing and configured to detect angular orientation of theorbital implant relative to the subject when the housing is disposedunder the eyelid of the subject and anterior to the orbital implant. Theprosthesis further includes a processor disposed within the housing andconfigured to determine, at least in part, a natural appearance for avisible portion of the eyeball of the subject based, at least in part,on the angular orientation of the orbital implant, and render, at leastin part, an image for presentation on the display based on the naturalappearance for the visible portion of the eyeball of the subject. Theocular prosthesis still further includes a power source disposed withinthe housing and configured to provide power for the display device, theimplant detector and the processor.

In a third set of embodiments, an ocular prosthetic system includes animplant marker configured to move with an orbital implant disposed in aneye socket of a subject, and an electronic ocular prosthesis. Theelectronic ocular prosthesis includes a housing having a form factorshaped to fit under an eyelid of the subject and in front of the orbitalimplant, wherein an anterior portion of the form factor is curvedsimilar to an anterior portion of a natural eyeball for the subject. Theelectronic ocular prosthesis also includes a display device disposedwithin the housing and visible at an anterior portion of the housing,and an implant detector disposed within the housing and configured todetect a position of the implant marker when the housing is disposedunder the eyelid of the subject and anterior to the orbital implant. Theelectronic ocular prosthesis further includes a processor disposedwithin the housing and configured to determine, at least in part, anatural appearance for a visible portion of the eyeball of the subjectbased, at least in part, on the position of the implant marker, andrender, at least in part, an image for presentation on the displaydevice based on the natural appearance for the visible portion of theeyeball of the subject.

In a fourth set of embodiments, a method includes determining a changein orientation of an orbital implant in a subject, and determining anupdate to a natural appearance for a visible portion of an eyeball forthe subject based on the change in orientation of the orbital implant.The method further includes rendering an update to an image of thenatural appearance for a display device disposed in an ocular prosthesisconfigured to be inserted in the subject anterior to the orbitalimplant.

In a fifth set of embodiments, an apparatus includes a housing and adetectable device. The housing includes a broad portion configured to beattached to an orbital implant or conjunctiva adjacent to the orbitalimplant. The detectable device is disposed in the housing adjacent tothe broad portion, and is configured to be detected remotely.

In other embodiments, an apparatus or computer-readable medium isconfigured to perform one or more steps of the above method.

Still other aspects, features, and advantages of the invention arereadily apparent from the following detailed description, simply byillustrating a number of particular embodiments and implementations,including the best mode contemplated for carrying out the invention. Theinvention is also capable of other and different embodiments, and itsseveral details can be modified in various obvious respects, all withoutdeparting from the spirit and scope of the invention. Accordingly, thedrawings and description are to be regarded as illustrative in nature,and not as restrictive.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is illustrated by way of example, and not by wayof limitation, in the figures of the accompanying drawings and in whichlike reference numerals refer to similar elements and in which:

FIG. 1 is a block diagram that illustrates a side view of an exampleocular prosthetic system including an orbital implant inserted within apatient eye socket and an ocular prosthesis in a non-inserted state,according to an embodiment of the present invention;

FIG. 2 is a block diagram that illustrates a side view of an exampleocular prosthetic system including an orbital implant inserted within apatient eye socket and an ocular prosthesis provided in an insertedstate adjacent and anterior to the orbital implant, according to anembodiment;

FIG. 3A is a block diagram that illustrates example components of anocular prosthesis, according to an embodiment;

FIG. 3B is a block diagram that illustrates example components of anocular prosthesis in a form factor suitable for insertion, according toan embodiment;

FIG. 3C is a perspective view that illustrates the example ocularprosthesis of FIG. 3A, according to an embodiment;

FIG. 4 is a block diagram that illustrates an example calibration devicein use for calibrating an ocular prosthesis, according to an embodiment;

FIG. 5 is a block diagram that illustrates an example calibration devicefor use in calibrating an ocular prosthesis, according to an embodiment;

FIG. 6A is a block diagram that illustrates an example ocular prostheticsystem that includes an ocular prosthesis and an orbital implantutilized by a patient that has undergone evisceration, where the ocularprosthesis is shown in an inserted state adjacent and anterior to theorbital implant, according to an embodiment;

FIG. 6B and FIG. 6C are block diagrams that illustrate example variousocular prosthesis systems, each with an external wearable device that isconfigured to perform one or more functions for the ocular prosthesis,according to some embodiments;

FIG. 7 is a flow diagram that illustrates an example method foroperating an ocular prosthesis with a display device, according to anembodiment;

FIG. 8 is a flow diagram that illustrates an example method forexternally calibrating and charging an ocular prosthesis with a displaydevice, according to an embodiment;

FIG. 9A and FIG. 9B are block diagrams that illustrate an exampledisplay device disposed in a housing having a form factor for an ocularprosthesis, according to an embodiment;

FIG. 9C is a block diagram that illustrates an example image forrendering on a display device, according to an embodiment;

FIG. 9D is a block diagram that illustrates an example screen forcontrolling properties of the image and image changes over time todetermine acceptable display properties, according to an embodiment;

FIG. 10A is a table that illustrates example power consumption for anelectronic display device suitable for an ocular prosthesis, accordingto various embodiments;

FIG. 10B is a graph that illustrates example recharge power for abattery suitable for an ocular prosthesis, according to an embodiment;

FIG. 11A through FIG. 11D are block diagrams that illustrate exampledetection of a magnet on the orbital implant with Hall Effect sensors onthe ocular prosthesis, according to an embodiment;

FIG. 11E through FIG. 11J are block diagrams that illustrate an examplemarker configured to be attached to the conjunctiva that moves with theorbital implant, according to various embodiments;

FIG. 12A through FIG. 12D are block diagrams that illustrate exampledetection of the orientation the orbital implant with sensors on theocular prosthesis that measure variable capacitance, according to anembodiment;

FIG. 12E and FIG. 12F are block diagrams that illustrate example factorsthat affect the measured variable capacitance, according to anembodiment;

FIG. 12G through FIG. 12L are block diagrams that illustrate exampledetection of a conductor moving with the orbital implant usinginductance sensors on the ocular prosthesis, according to an embodiment.

FIG. 13A is a block diagram that illustrates an example radius of afield of view of a photodiode disposed in the ocular prosthesis,according to an embodiment;

FIG. 13B is a block diagram that illustrates example distribution ofphotodiodes disposed in the ocular prosthesis to detect movement of animplant marker that moves with the orbital implant and emits light,according to an embodiment;

FIG. 13C and FIG. 13D are block diagrams that illustrates exampleoverlapping fields of view of multiple photodiodes disposed in theocular prosthesis, according to various embodiments;

FIG. 14A through FIG. 14C are block diagrams that illustrate exampletest equipment used to demonstrate determining experimental orbitalimplant movement based on an light emitting implant marker andphotodiodes arranged as on an ocular prosthesis, according to anembodiment;

FIG. 15A is a table that illustrates example variation of detected lightintensity with angular separation between photodiode and light emittingimplant marker, according to an embodiment;

FIG. 15B through FIG. 15E are graphs that illustrate example variationsof detected light intensity with angular separation between photodiodeand light emitting marker on a experimental orbital implant, accordingto various embodiments;

FIG. 16A is a photograph that illustrates an example test equipmentcircuit board configured to measure relative intensity at multiplephotodiodes to determine orientation of the experimental orbitalimplant, according to an embodiment;

FIG. 16B is a block diagram that illustrates an example circuit on acircuit board of FIG. 16A configured to measure relative intensity atmultiple photodiodes, according to an embodiment;

FIG. 16C is a table that illustrates example power consumption ofvarious components of the optical sensor circuitry, according to someembodiments;

FIG. 17A and FIG. 17B are graphs that illustrate example variations ofdetected light intensity with positive and negative angular separationsbetween photodiode and light emitting marker on an experimental orbitalimplant using the circuit of FIG. 16B, according to various embodiments;

FIG. 18A is a block diagram that illustrates an example arrangement ofphotodiodes to detect motion of a experimental orbital implant with alight emitting marker, according to an embodiment;

FIG. 18B is a graph that illustrates example orientation confidence forthe experimental orbital implant using the photodiode arrangement ofFIG. 18A, according to an embodiment;

FIG. 19A and FIG. 19B are graphs that illustrates example distributionsof errors with distance between light emitting marker and photodetectorsused to triangulate position of the marker, according to an embodiment;

FIG. 20 is a block diagram that illustrates example disposition, in avertical cross section, of components of an ocular prosthesis in ahousing with a form factor suitable for insertion as an ocularprosthesis under an eyelid of a subject and anterior to an orbitalimplant, according to an embodiment;

FIG. 21 is a block diagram that illustrates a computer system upon whichan embodiment of the invention may be implemented;

FIG. 22 illustrates a chip set upon which an embodiment of the inventionmay be implemented;

FIG. 23A and FIG. 23B are block diagrams that illustrate assembly of anexample array of photodetectors for implant marker detection for aspatial model of the ocular prosthesis, according to an embodiment;

FIG. 23C is a block diagram that illustrates a detail of an exampleanterior face of one photodetector array element, according to anembodiment;

FIG. 24A through FIG. 24D are block diagrams that illustrate an examplespatial model of an ocular prosthesis, according to an embodiment; and

FIG. 25A and FIG. 25B are block diagrams that illustrate an exampleshaped battery component of the spatial model of an ocular prosthesis,according to an embodiment.

DETAILED DESCRIPTION

A method and apparatus are described for an ocular prosthesis with adisplay device. In the following description, for the purposes ofexplanation, numerous specific details are set forth in order to providea thorough understanding of the present invention. It will be apparent,however, to one skilled in the art that the present invention may bepracticed without these specific details. In other instances, well-knownstructures and devices are shown in block diagram form in order to avoidunnecessarily obscuring the present invention.

Some embodiments of the invention are described below in the context ofa self-contained ocular prosthesis with an electronic display working inconcert with a marker configured to move with an orbital implant.However, the invention is not limited to this context. In otherembodiments some of the functions of the ocular prosthesis (such aspower storage or data processing or ambient light detection or implantorientation detection or natural eye orientation detection) areperformed in a wearable device external to the ocular prosthesis orexternal to both the orbital implant and the ocular prosthesis, or themarker is omitted, or the orbital implant is omitted, or motion of theremaining natural eye is tracked, or a mechanical display or chemicaldisplay is used instead of, or in addition to, an electronic display orthe system is changed in some combination of ways.

1. OVERVIEW

Various embodiments of the ocular prosthetic system described herein canbe provided to patients as a new prosthesis, or a patient's existingimplant or prosthesis can be retrofitted to incorporate features of theinvention. Certain groups of patients may require variations on theorbital implant and the associated procedures. For example, one groupincludes those who are newly fitted with an orbital implant (which ispreferentially anchored to the muscles), and another group includesthose who already have an orbital implant and, in lieu of replacing theexisting implant with a new orbital implant, patients in this group canbe retrofitted. As used herein, the term subject is used to refer to amachine an organism that hosts the ocular prosthesis system, whether ahuman patient or an animal patient or a test animal or a volunteer ofsome sort or a robot.

FIG. 1 is a block diagram that illustrates a side view of an exampleocular prosthetic system including an orbital implant 120 insertedwithin a subject eye socket 12 and an ocular prosthesis 110 in anon-inserted state, according to an embodiment of the present invention.The orbital implant 120 is surgically inserted within a subject eyesocket 12 within the subject skull 10. FIG. 2 is a block diagram thatillustrates a side view of an example ocular prosthetic system includingan orbital implant 120 inserted within a subject eye socket 12 and anocular prosthesis 110 provided in an inserted state adjacent andanterior to the orbital implant 120, according to an embodiment.

Generally, the orbital implant 120 is capable of movement, albeit notalways full movement; the movement can vary from subject to subject.Degree of movement (called motility herein) depends on whether or notthe orbital implant 120 is attached to the muscles 18, and also on thedifferences in movement capability of the muscles which are attached. Insome subjects, a firm capsule forms around the implant 120 and themuscles 18 naturally attach to the capsule allowing the orbital implantto move. The movement of the implant is rarely comparable to themovement in the unaffected eye. In some subjects, the conjunctiva 14surrounds the implant 120 and moves with the implant 120.

A closed loop of tissue (the prosthesis space) is formed by theconjunctiva 14 covering the implant and the fornices 15 above and below,and the undersurfaces of the eyelids 16. A fornix is generally the pouchlike space between the undersurface of the eye lid and eyeball intowhich a prosthesis sits. Even with complete movement of the orbitalimplant 120 in response to muscles 18, an inserted ocular prosthesis 110is constrained by this closed loop of tissue that prevents realisticmotility. Thus, in various embodiments, the ocular prosthesis includesan electronic display device or mechanical facsimile that mimics naturalmovement of an iris and or pupil and or blood vessels normally visibleto an observer—even though movement of the ocular prosthesis 110 itselfis limited or absent.

The embodiment depicted in FIG. 1 and FIG. 2 includes an implant marker122 (such as a tattoo, or a magnet, or non-magnetic foil or lightemitter, as described in some detail below, or some combination, invarious embodiments) provided within or retrofitted to be included on orwithin the orbital implant 120 or the conjunctiva 14 that cover theimplant 120. In this embodiment, a sensor (such as a Hall Effect sensorfor the inserted magnet or a second foil or a photodiode, or some othersensor, alone or in combination) provided within the ocular prosthesis110 senses the relative motion between the implant marker 122 on theorbital implant 120 and the ocular prosthesis 110, which allows aprocessor within the ocular prosthesis to determine the intended,lifelike motion of the eye using predetermined calibration measurements,as will be described in greater detail below. The Hall Effect wasdiscovered by Edwin Hall in 1879, and it generally refers to theproduction of a voltage difference (the Hall voltage) across anelectrical conductor, transverse to an electric current in the conductorand a magnetic field perpendicular to the current. The ocular prosthesis110 then utilizes this data to render on a display device (e.g.,electronically or mechanically or chemically, or some combination)lifelike motion of an eye. Additionally, a light sensor provided on theocular prosthesis is used in some embodiments to sense an ambient lightlevel, and the ocular prosthesis 110 can then utilize this data torender on the display device (e.g., electronically or mechanically orchemically) lifelike size/adjustment of the pupil of the eye.

Thus, in the embodiment depicted in FIG. 1 and FIG. 2, the orbitalimplant 120 for a newly fitted subject contains a marker 122 which canbe coated in biocompatible material, such as an epoxy, among others. Forretrofit subjects, a “retrofit kit” is provided to a doctor performingthe retrofitting. In such a kit, the marker is injected by needle orplaced in a hole cut with a drill to insert the marker into an orbitalimplant already in place, or the marker is placed in a bio-compatibletube that is then closed at each end and sutured or otherwise allowed tobecome embedded in the conjunctiva 14 or scar-conjunctival complexoverlying the orbital implant 120.

FIG. 3A is a block diagram that illustrates example components of anocular prosthesis 110, according to an embodiment. FIG. 3B is a blockdiagram that illustrates example components of an ocular prosthesis 110in a housing having a form factor suitable for insertion into theprosthesis space, according to an embodiment; and FIG. 3C is aperspective view that illustrates the example ocular prosthesis 110 ofFIG. 3A, according to an embodiment. Note that while the depiction inFIG. 3C is in grayscale, the ocular prosthesis 110 can be provided withnatural eye coloring in order to appear lifelike (also called naturalherein).

In the embodiment depicted in FIG. 3A and FIG. 3B, In variousembodiments, the ocular prosthesis includes a display device 311. Thedisplay device is arranged in the ocular prosthesis to be visible at ananterior portion of the housing. In some embodiments, the display is aflat display with lenses arranged to simulate curvature of the anteriorportion of a natural eyeball. In some embodiments, the display is a flatdisplay that uses software instructions to transform the image tosimulate the appearance of movement of an iris along a curved surface.In some embodiments, the display is a flexible display that is bent intoa horizontally curved and vertically curved surface. In someembodiments, the display is a flexible display that is bent into ahorizontally curved surface. In some embodiments the display is anemissive display that emits light. In some embodiments, an emissivedisplay is configured to emit different amounts of light under differentlighting conditions to reduce glow in low light conditions. In someembodiments, the display is a reflective display that merely absorbssome colors and reflects other colors of ambient light that impinges onthe display. Such displays have the advantage that they do not appear toglow in low light conditions, and thus appear more natural. In someembodiments, the prosthesis contains a mechanical facsimile of the iristhat uses mechanical means to simulate movement of a facsimile of thesubject's healthy eye. A mechanical pupil is also envisioned with thispossibility. In some embodiments, the mechanical means include smallmotors that physically move the iris throughout its intended range ofmotion within the prosthesis. Pupil response is initiated with motorsmoving a mechanical iris similar to the aperture mechanism in a cameralens with “leaves,” or alternatively with some electrically responsivematerial that expands and contracts based on an electrical input.

In the illustrated embodiment, the ocular prosthesis also includes animplant detector 309 and a processor 301. The illustrated embodimentalso includes a power source 302 that includes a power storage/supplyunit 303 (e.g., a battery) and a charge receiving device 305 (e.g., ainductive charge receiving device that can be wirelessly charged using aseparate inductive charging station, or a charge receiving device havingelectrical contact for wired connection to a charging station, amongothers). For example, in some embodiments the charge receiving device305 includes an induction coil. The illustrated embodiment of the ocularprosthesis 110 also includes a light sensor 307 (e.g., a photovoltaiccell, a photoresistor, an optical detector, or a photodiode, amongothers, or some combination). The illustrated embodiment of the ocularprosthesis 110 also includes a communication module 313 (e.g., contactsfor a wired transceiver or an antenna with or without a tuning circuitfor a wireless receiver or transceiver).

In various embodiments, the communication module 313 is a communicationcomponent that can communicate with a programming unit in order toreceive calibration information, software, or other data that can beutilized by the other components such as the processor 301, amongothers. For example, in some embodiments, the communication module 313includes an antenna for picking up signal sent as an electromagneticwave. In some embodiments, the antenna of communication module 313doubles as an induction coil for the charge receiving device 305.

In various embodiments, the processor 301 is configured as a chip setwith a microprocessor and a memory, as described in more detail belowwith reference to FIG. 22. In some embodiments, the processor 301 isconfigured to receive various data from the communication module 313,the light sensor 307, and the implant detector 309, and then sendcontrol signals to the display device 311 in order to have the displaydevice 311 provide a lifelike display (e.g., color, motion of theiris/pupil, size of the iris/pupil, or presence/prevalence of bloodvessels, among others, alone or in some combination).

In some embodiments, there is a coating on the ocular prosthesis. Insome embodiments, the ocular prosthesis is made of methylmethacrylate,with the various components, such as the electronic parts and lightsensor, embedded within this plastic. In various embodiments, the ocularprosthesis is waterproof.

In various embodiments, the implant detector 309 includes one or moresensors to provide an accurate detection of the relative movementbetween the implant marker 122 and the ocular prosthesis 110. In variousembodiments, the display device 311 is configured to present acomputer-generated image of a visible portion of an eye of the subject,which is visible over at least a portion of the anterior surface of theocular prosthesis 110 as shown in FIG. 3B and FIG. 3C. In variousembodiments, one or more features of the image representing the naturalappearance of an eye of the subject are controlled in order to provide anatural appearance with lifelike eye features and motions. In someembodiments, a charging station is provided to the subject by which thesubject can charge the power source 302 of the ocular prosthetic system110 via the charge receiving device 305. For example, in someembodiments, the power source is recharged by removing the ocularprosthesis 110 from the subject's body and connecting (either wirelesslyor via wired connection) the ocular prosthesis 110 to the charger of acharging station for a period of time (e.g., overnight) sufficient toprovide operation for all or most of the remaining day.

In various embodiments, the power storage/supply unit 303 is any type ofbattery. In some embodiments, the ocular prosthesis 110 is powered bysome external source of energy, e.g., in a wearable device, thusremoving the need for one or both of an internal power storage/supplyunit 303 and charge receiving device 305. For example, in someembodiments, the ocular prosthesis is powered using microwaves (e.g.,making use of radiation from cell-phones or other external device);while, in some embodiments, the ocular prosthesis is powered byconverting the subject's body's own heat into electricity.

FIG. 4 is a block diagram that illustrates an example calibration devicein use for calibrating an ocular prosthesis, according to an embodiment,and FIG. 5 is a block diagram that illustrates an example calibrationdevice for use in calibrating an ocular prosthesis, according to anembodiment.

In the illustrated embodiment, the calibration device 400 is asupporting external auxiliary device for the ocular prosthetic system100. As seen in FIG. 4, the calibration device 400 includes a housing402, which can be in the form of a pair of glasses or table-mounted,adjustable eye examination unit, among others. While the calibrationdevice 400 shown in FIG. 4 only depicts a sensing of the orbitalimplant, it should be noted that the calibration device 400 can seriallyor simultaneously also sense the movement of the other eye of thesubject (e.g., in order to help calibrate the display of the ocularprosthesis by determining the motility of the subject's other eye) inorder to match the motion of the display of the ocular prosthesis 110 tothe motion of the subject's other eye, whether it is also a prosthesisor not. As shown in FIG. 4, the calibration device 400 sends light 404and receives light 406 (or simply receives ambient light reflecting off)from the orbital implant 120 in order to sense the motion of the orbitalimplant 120 for calibration purposes. This procedure may also beperformed with the ocular prosthesis 110 in the inserted state forcalibration, in some embodiments. Such a measurement with the ocularprosthesis 110 in the inserted state can also be used in conjunctionwith the measurements in the non-inserted state, in order to account forany motion of the ocular prosthesis 110 within the closed loop of theprosthesis space in front of the orbital implant when determining theproper calibration of the display.

The calibration device 400 provides a way to measure the movement of theunaffected eye (the movement in all directions), and also provides a wayto detect the color of the normal eye of the subject and the response ofthe pupil to light, and take this information and use this to direct thedisplay of the ocular prosthesis 110 in order to program the controllersof the display device on how to have the image appear to “behave.”

As shown in FIG. 5, an embodiment of the calibration device includes aprocessor 501, one or more scanners 503, for example to detect motion(e.g., direction of the motion, speed of the motion, acceleration of themotion), color, and other features of the normal eye or the eye beingfitted with a prosthesis (e.g. a pupil velocity meter), a data storagedevice 505 for storage of measurement data, and other configurationdata, and a user interface 507 to allow an operator (such as the doctoror technician) to control the operation of the calibration device andprocessing of the measurements taken. The illustrated embodiment of thecalibration device 400 also includes a communication device 513 that isconfigured to wirelessly (or via wires) communicate with thecommunication module 313 of the ocular prosthesis 110 in order toprovide calibration information, including factors to correct theorientation, motion and other appearance shown by the ocular prosthesis110. In some embodiments, the calibration device 400 also includes acharging station 512 that is configured to wirelessly (or via wires)provide power to the power source 302 on the ocular prosthesis 110.

For example, the following non-limiting, example of a calibrationprocedure is followed in some embodiments once the implant/prosthesis isfitted. For example, a picture of the eye before removal or of thesubject's other eye (e.g., if the subject's other eye is healthy) can bescanned for color (high resolution digital image). Also, in someembodiments, a movement calibration is performed in order to measure oneeye against the other by instructing the subject to look in a range ofdirections. For example, the subject is instructed to look as far leftas possible and the degrees from center are measured for the unaffectedeye, and measured for the orbital implant or the eye image (or somecalibration point) on the ocular prosthesis. Measurement data of suchmovements is recorded by the calibration device 400, and communicated tothe ocular prosthesis 110 through communication module 313. Theprocessor 301 in the ocular prosthesis 110 is then programmed tocompensate so that the image on the display will act in the same manneras the unaffected eye. For example, if the marker on the orbital implantcan only be shifted five degrees to the left by muscle movement, but thenormal eye can look thirty degrees to the left, then the calibrationalgorithm will indicate that this five degrees of movement scales sothat the image appears to move thirty degrees. In some embodiments, thecalibration device is worn like a pair of glasses that measures theunaffected eye movement and response as a standard, and then directs theprocessor in the ocular prosthesis. In some embodiments, the movementscan be measured using the calibration device with the ocular prosthesis110 in the inserted state. The ocular prosthesis is then removed (to thenon-inserted state) and connected to the calibration unit in order tosynchronize the calibration measurements with the processor of theocular prosthesis.

In various embodiments, software executing on a processor is utilized toimplement embedded controls for the hardware on the ocular prosthesis,as well as for the various control systems for motion control of theeye. In some embodiments, fuzzy logic is used for designing a realisticpupil response to incident light. In various embodiments, microprocessorprogramming is written utilizing a Hi-Tech C compiler along with a MPLABsuite of tools from the Microchip Corporation line of microcontrollers.In various embodiments, the microcontroller is an 8 bit 4 MIPS unit, ora 16 bit MIPS for increased performance, among others, or somecombination.

In some embodiments, the ocular prosthetic system is configured toprovide a computerized image of an iris with realistic conjunctivalblood vessels, which moves like a human eye, is colored to match a humaneye, and responds to ambient light levels. In some embodiments thedisplay device is a screen mounted into a molded methylmethracylateprosthesis with a form factor suited for insertion under the subject'seyelid and adjacent and anterior to the surgically implanted orbitalimplant. These prostheses can be molded, for example, utilizing dentalprosthodontic techniques. A mold of the subject's anophthalmic socket(socket without an eye) is made, in some embodiments, utilizingalginate; and, the mold is transferred into plastic.

The ocular prosthesis itself (with embedded display device) isconfigured to respond to movement of the surgically implanted orbitalimplant on or into which zero or more markers have been placed. In someembodiments, motion sensing technology is utilized to detect themovement of the marker(s), and the ocular prosthesis is individuallyprogrammed so that horizontal movement of the embedded marker translatesinto horizontal movement of the image on the display device disposedwithin the ocular prosthesis, and similarly vertical movement detectedin the implant translates into vertical movement of the image on thedisplay device.

Various embodiments of the invention provide a miniaturized, functional,multicolor, embedded, powered electronic or mechanical prosthesis andequipment that can convert movement of the embedded implant into lifelike movement of the image displayed by the prosthesis.

Enucleation is generally the surgical removal of the entire eye butleaving the six extraocular muscles and part of the optic nerve. Asdiscussed above and shown in FIG. 1, the ocular prosthetic system can beutilized by a subject that has undergone surgical enucleation.

Additionally, the ocular prosthetic system can be used after a techniquecalled “evisceration.” An evisceration is a surgical procedure by whichonly partial removal of the eye is performed (e.g., such a procedure canbe performed after trauma to the eye). The front half of the eye isremoved and the contents inside the eye removed but the sclera, musclesand optic nerve (and supplying blood vessels) are left. In thissituation, in some embodiments, an orbital implant is then placed intothe remaining half of the eye, and the ocular prosthesis used therewith.FIG. 6A is block diagram that illustrates an example ocular prostheticsystem that includes an ocular prosthesis and an orbital implantutilized by a subject that has undergone evisceration, where the ocularprosthesis 110 is shown in an inserted state adjacent and anterior tothe orbital implant 120, according to an embodiment. The orbital implant120 is surgically inserted within the remaining half of the eye 600. Inthis situation, the muscles 18 around the eye (six of them) typicallyremain connected to the remaining half of the eye 600.

In some embodiments, the ocular prosthetic system is available inseveral sizes to account for all size variations of subjects (infantsthrough adults). This enables a practitioner to continue to provide aproperly sized prosthesis to mimic natural volume, while allowing thecomputerization to account for movement, esthetics, and pupildilatation.

In a further alternative embodiment, velocity and/or accelerationsensors are included in the implant detector 309. For example, one ormore velocity and/or acceleration sensors are provided in the ocularprosthesis 110, and one or more velocity and/or acceleration transducersare provided in the orbital implant 120 in order to allow the ocularprosthesis 110 to detect and emulate the intended, lifelike motion ofthe eye using scaling factors based on calibration measurements. Invarious embodiments, the velocity/acceleration sensors or portionsthereof are put into the orbital implant and/or ocular prosthesis tosense movement of the orbital implant and/or ocular prosthesis, and theocular prosthesis 110 receives and utilizes this data to displaylife-life motion of an eye. For example, an embodiment includes such asensor in both the orbital implant and the ocular prosthesis, and theocular prosthesis uses output signals from both such sensors to cancelout any outside movement of the body of the person and only use relativemovement between the orbital implant and ocular prosthesis to move theeye display. In some such embodiments, the output signal is wirelesslytransmitted from the orbital implant by a transmitter therein to areceiver in the ocular prosthesis.

FIG. 6B and FIG. 6C are block diagrams that illustrate example variousocular prosthesis systems, each with an external wearable device 620 or640 that is configured to perform one or more functions for the ocularprosthesis 610, according to some embodiments. For example, in variousembodiments, an earpiece device 620 resting on an ear, e.g., an earclosest to the ocular prosthesis 610, or a portion 640 of a frame of apair of glasses closest to the ocular prosthesis 610, houses one or morecomponents that augment or replace components depicted in FIG. 3A forthe ocular prosthesis 110 or one or more components of the calibrationdevice 400 depicted in FIG. 5, or some combination. Power andinformation are transferred to the ocular prosthesis 610 through one ormore wired or wireless means, e.g., one or more tiny skin colored wiresor one or more antenna and induction coils.

Although processes, equipment, and data structures are depicted in FIG.3A, FIG. 3B, FIG. 5, FIG. 6B and FIG. 6C, as integral blocks in aparticular arrangement for purposes of illustration, in otherembodiments one or more processes, equipment or data structures, orportions thereof, are arranged in a different manner, on the same ordifferent hosts, in one or more databases, or are omitted, or one ormore different processes or data structures are included on the same ordifferent hosts. For example, a processor in earpiece 620 or frameportion 640 includes one or more processors or power sources or memoryto replace or assist the functions of those components in FIG. 3A andFIG. 5.

FIG. 7 is a flow diagram that illustrates an example method 700 foroperating an ocular prosthesis with a display device, according to anembodiment. Although steps are depicted in FIG. 7, and in subsequentflowchart FIG. 8, as integral steps in a particular order for purposesof illustration, in other embodiments, one or more steps, or portionsthereof, are performed in a different order, or overlapping in time, inseries or in parallel, or are omitted, or one or more additional stepsare added, or the method is changed in some combination of ways.

In step 701, one or more implant markers are attached to move with anorbital implant. For example, as described above, in variousembodiments, a hole is drilled in an implant, either before or after theorbital implant is surgically attached to one or more optic muscles 18,and a marker, such as a magnet or light emitting diode is inserted inthe hole and sealed in. In other embodiments, the marker, such as one ormore tattoos or one or more foils for a variable capacitor, as describedin more detail below, are attached to an outside of the orbital implantand sealed in place. The conjunctiva may then subsequently form over theseal. In some embodiments, no marker is required, and step 701 isomitted.

In some embodiments, during step 701, the marker is attached to theconjunctiva that moves more or less with the orbital implant; but, themarker is not directly attached to the implant. In some of theseembodiments, as described in more detail below, step 701 includesinserting the one or more markers into a tube of biologically inertmaterial, such as silicone or some type of plastic, either before orafter one end of the tube has been closed, e.g., by crimping or heat.Then the remaining end or ends of the tube are closed and the tube withenclosed ends is sutured to the conjunctiva or scar-conjunctiva complexthat forms over the orbital implant. Such placement of the implantmarker is especially suitable for retro fitting an implant alreadysurgically attached, or replacing markers after their useful lifetime.This and other alternatives for the marker, such as a paddle marker, aredescribed in more detail below with reference to FIG. 11E through FIG.11J.

In step 703, the power source on the ocular prosthesis is charged orconfiguration data is sent to the processor/memory in the ocularprosthesis, or both. In some embodiments, step 703 is performed beforestep 705, while the ocular prosthesis 110 is in a non-inserted stated,as depicted in FIG. 1. For example, in some embodiments, the ocularprosthesis is placed in a charging station for a suitable period oftime. In some embodiments, step 703 is performed after step 705, whilethe ocular prosthesis 110 is in an inserted state, as depicted in FIG.2. For example, the calibration device 400 or earpiece 620 or glassesframe portion 640 emits an electromagnetic wave that produces a currentin an induction coil in a charge receiving device 305 of the powersource 302, as well as in an antenna of the communications module 313.In some embodiments, contacts on a surface of the ocular prosthesis areconnected by wires to a charging station, such as calibration device400, earpiece 620 or glasses frame portion 640, or some combination,during step 703.

In some embodiments, configuration data comprises an image or acompressed image of a natural eye for the subject, or some combination.In some embodiments, the configuration data includes values for variousparameters, such as a size for the iris, a color selected from a limitedcolor palette, or a particular combination of a limited color palette, asize range for a pupil, a rate of change for a pupil, and scalingfactors for transforming detected motion of the orbital implant intonatural motion (e.g., angular range and speed and or acceleration) ofthe iris. In some embodiments, configuration data includes values forparameters used by the implant detector, such as spacing associated withphotodiodes and light intensity calibration data. In some embodiments,configuration data includes software instructions to cause the processorto perform one or more functions, and calibration data for one or moreother sensors, such as ambient light sensor or accelerometer or sensorto determine orientation in gravity field. Further detailed examples ofconfiguration data are described below in the context of one or moreembodiments with various display devices and implant detectors.

In some embodiments, step 703 includes operating the calibration device400 to determine one or more properties of the image or scaling factors,as described in more detail below with reference to FIG. 8. For example,during an initialization phase, the calibration device 400 is operatedto observe the other eye of the subject, either alone or in concert witha marker on the orbital implant or ocular prosthesis, to determineinitial scaling factors, properties of the appearance of the other eyeor some combination. In some embodiments, step 703 includescommunicating software instruction upgrades for the processor 301 in theocular prosthesis 110.

In step 705, the ocular prosthesis is inserted into the prosthesis spaceunder the eyelids and anterior to the orbital implant. When insertedinto the prosthesis space, the ocular prosthesis is herein described tobe “adjacent” to the orbital implant. However the prosthesis may or maynot be in contact with the orbital implant or the conjunctiva orscar-conjunctiva complex. However, when adjacent to the orbital implant,an implant detector disposed in the ocular prosthesis, in someembodiments, is within range to detect the orbital implant or any markerthat moves with the orbital implant.

The following steps from step 711 through step 721 are performed, invarious embodiments by the ocular prosthesis acting alone, or incombination with an external wearable device, such as earpiece 620 orglasses frame portion 640, or some combination.

In step 711, the configuration data sent in step 703 is received. Theconfiguration data is configured to indicate one or more properties forrendering a natural appearance for an eyeball on the display device 311disposed in the ocular prosthesis. Example configuration data aredescribed above with reference to step 703.

In step 713, the position or movement of the orbital implant, or othereye, is detected. In several illustrated embodiments described below,different implant detectors are described. In some embodiments, step 713includes detecting orientation or motion of natural or other eye, e.g.,using one or more sensors disposed in earpiece 620 or glasses frameportion 640, or some combination. In some embodiments, absoluteorientation is not utilized, and only changes in orientation or rate ofchange of orientation are detected during step 713. In some embodiments,step 713 involves detecting one or more markers. In some embodiments,step 713 involves detecting mechanical sliding of conjunctiva past theocular prosthesis, such as used in an optical computer mouse pointingdevice, without a marker attached to the implant. In some embodiments,step 713 includes activating the marker 122 that moves with the orbitalimplant, or powering the marker 122, or some combination, as describedin more detail below with regard to a particular embodiment. Thus,during step 713, a change is determined in orientation of an orbitalimplant in a subject.

In step 715, the ambient light detected on an anterior surface of theocular prosthesis is determined. For example, based on output from lightsensor 307, the ambient light level in the neighborhood of theprosthesis is determined and provided as a specific value of the lightintensity or a code representing same. In some embodiments, the lightsensor 307 is omitted and step 715 is likewise omitted.

In step 717, an update is determined for the natural appearance of avisible portion of an eyeball for the subject based on the position ormovement of the orbital implant or ambient light or some combination.For example, movement of the center of the iris is determined bothhorizontally and vertically based on the change or movement in theorientation of the orbital implant and change in size of the pupil isdetermined based on the ambient light level. Thus, in step 715, anupdate is determined to a natural appearance for a visible portion of aneyeball for the subject based on the change in orientation of theorbital implant.

In step 719, the natural appearance of the visible portion of theeyeball of the subject is rendered on the display device 311. Any methodknown in the art to render an image may be used. As described in moredetail below, the display device is configured with a certain number ofpixels in the horizontal and vertical dimensions and with a certainrefresh rate. For example, instructions and power are sent to operatevarious pixels of the display device 311 as described in more detailbelow. Only the pixels that are affected by the change determined instep 717 over a time interval corresponding to the refresh rate areupdated in some embodiments. In some embodiments, a new image isdetermined entirely at the refresh rate. In other embodiments, based onthe previous image and the changes in position of the orbital implant orambient light, only pixels that are affected by the change are updated.In some embodiments, such as embodiments using the Motion PictureEngineering Group (MPEG) protocol, panels of the image that are affectedby the change and the changes to those panels are determined andrendered on the display device 311. Thus step 719 includes rendering anupdate to an image of the natural appearance for a display devicedisposed in an ocular prosthesis configured to be inserted in thesubject anterior to the orbital implant.

Various efficiencies are implemented in various embodiments. Forexample, as described in more detail below, in some embodiments, only afew bits are utilized to represent the color at each pixel based on areduced color palette. In some embodiments, the reduced color paletterefers only to colors enabled to render the appearance of the eye of aparticular subject. In some embodiments, the reduced color paletterefers to colors enabled to render the appearance of the eye of alimited population of subjects, such as brown eyed subjects or blue-eyedsubjects. In some embodiments, the reduced color palette refers tocolors enabled to render the appearance of all possible subjects. Evenso, the number of colors in the palette is substantially less than thenumber of colors used in photographic imagery because many colors arejust not found among the iris colors of the population of subjects.

In step 721, the various components disposed in the ocular prosthesisare operated to conserve power. In general, step 721 is performedsimultaneously with step 713 through step 719. For example, in someembodiments, display device 311 is a reflective display device thatrequires little power to retain an image and consumes power only whenthe value at a pixel is changed in an amount that depends on the numberof pixels changed. In such embodiments, the circuits that power eachpixel are deactivated between refresh events.

In some embodiments, the following steps from step 723 through step 733are performed by an operator of the ocular prosthesis system, such asthe subject, a care giver, a technician or a practitioner.

In step 723, it is determined whether a wear cycle has ended. If not,then control returns to step 713 and following steps to determining anupdated position of the orbital implant 120 or other eye and updatingthe display device 311. In some embodiments, it is determined fromrecent orientations of the orbital implant or other eye, that theorbital implant or other eye is not moving; and, the time to cyclethrough steps 713 and following is extended. In some of theseembodiments, when it is determined that the orbital implant or other eyeis moving, the time to cycle through step 713 and following is decreasedbased on the rate of movement of the orbital implant or other eye downto the shortest time associated with the refresh rate of the displaydevice 311.

If it is determined in step 723 that they wear cycle has ended, then instep 731 the ocular prosthesis is removed from the subject's eye, e.g.is removed from the prosthesis space behind the subject's eyelids and infront of the orbital implant. In some embodiments, the subjectdetermines that the wear cycle has ended, e.g. at the end of the day,and the subject removes the ocular prosthesis. In some embodiments,depletion of power from the power source determines that the wear cyclehas ended; and, the subject is alerted to remove the ocular prosthesis,e.g., by an audible sound or a vibration.

In step 733, it is determined whether the ocular prosthesis should berecharged or recalibrated. If not, the process ends. If so, then controlpasses back to step 703 to recharge the power source or send newconfiguration data, or some combination.

FIG. 8 is a flow diagram that illustrates an example method 800 forexternally calibrating and charging an ocular prosthesis with a displaydevice, according to an embodiment. In step 801, the appearance of theocular prosthesis and the appearance of the other eye (natural or not)are observed simultaneously, e.g. using the calibration device 400 orsimilar components in earpiece 620 or glasses frames 640. In someembodiments, in step 801, movement of the orbital implant is detectedalong with, or in place of, the appearance of the ocular prosthesis. Forexample, in some embodiments, digital video is collected from each eyewhile the subject executes one or more movements for calibrationpurposes, such as rolling eyes left and right as well as up-and-down tothe maximum extent possible.

In step 803, difference in appearances of the ocular prosthesis and theother eye are determined. In some embodiments, step 803 includesdetermining a difference between movement of the orbital implant and theother eye in addition to or instead of determining the difference fromthe appearance of the ocular prosthesis. For example, the digital videoof each eye collected during step 801 are registered to each other, e.g.by the center of the pupil, and two dimensional correlation coefficientsare determined as a function of time.

In step 805, a first factor is determined. The first factor relatesmovement of an image of an eyeball on display device 311 of the ocularprosthesis to the detected movement of the orbital implant 120. Themovement of the orbital implant 120 can be detected directly by thecalibration device 400, or indirectly through movement of the image onthe display device 311 of the ocular prosthesis 110. In someembodiments, the first factor is a vector of values representingdifferent directions or rates of change, or some combination. Forexample, in some embodiments the values of the vector of the firstfactor are determined such that the two dimensional correlationcoefficients of the scaled video of the image of the ocular prosthesiswith the video of the other eye are maximized.

In step 807, a second factor is determined. The second factor relates achange in a size of the pupil to the change in amount of detectedambient light. The change in amount of detected ambient light can bedetected directly by the calibration device 400, or indirectly throughcommunication of the output of the ambient light sensor 307 from theocular prosthesis 110 or size of the pupil on the display device 311 ofthe ocular prosthesis 110. In some embodiments, the second factor is avector of values representing different light levels or rates of change,or some combination.

In step 809, the first and second factors are communicated as part ofthe configuration data transmitted by communication module 513 to theocular prosthesis 110, as received during step 711, described above. Asalso described above, in some embodiments the configuration datatransmitted by communication module 513 during step 809 also includesone or more properties of the natural appearance of a visible portion ofan eyeball of the subject, such as iris size and color, pupil size andrange of sizes, and position or density of blood vessels apparent on thesclera. In some embodiments, the configuration data includes softwareinstructions for the processor 301 on the ocular prosthesis 110.

In step 811, a power source for the ocular prosthesis or for the orbitalimplant or both is charged. For example, an antenna or coil in chargingstation 512 of calibration device 400, or equivalent components inearpiece 620 or glasses frame portion 640, wirelessly induces a currentin an induction coil in the ocular prosthesis, or orbital implant, ormarker 122 that moves with the orbital implant 120, or some combination.In some embodiments, the charging station 512, or equivalent componentsin earpiece 620 or glasses frame portion 640, is connected by wires tocontacts on the ocular prosthesis 110 or orbital implant 120 or marker122 that moves with the orbital implant 120, or some combination. Apower source for the charging station 512, or equivalent components inearpiece 620 or glasses frame portion 640, is engage to transmit powerto the device being charged.

In step 821, it is determined whether conditions are satisfied torecalibrate the ocular prosthesis 110. For example, in some embodiments,the conditions to recalibrate include the current time reaching aparticular scheduled date for recalibration, or notification that anupdate to software is available, or replacement of the ocular prosthesis110, or receiving error messages from the ocular prosthesis during step809, or upon the recommendation for recalibration from a practitioner ortechnician who has examined the operation of the ocular prosthesis inthe subject, among others, or some combination. If conditions aresatisfied for recalibration, then control passes back to step 801 andfollowing steps. If not, control passes to step 823.

In step 823, it is determined whether conditions are satisfied torecharge the ocular prosthesis 110. If so, then control passes back tostep 811. If not, then the process ends.

Using the methods 700 and 800, or portions thereof, with ocularprosthesis 110 and calibration device 400, respectively, it is possibleto accurately scale movement of an image of an eye to match the movementof a natural eye of a subject. Orbital implant motion is calibrated,compensating for any physiological movement limitations as a result ofthe surgery that attached the orbital implant 120 to the eye muscles 18.A digital image of an iris is determined with realistic conjunctivalblood vessels, which is color matched to the human eye, and whichaccurately moves like a human eye with a realistic and dynamic responseto ambient light.

2. EXAMPLE EMBODIMENTS

In this section, various specific embodiments of one or more componentsof the ocular prosthesis system are described, along with results of oneor more experimental embodiments.

2.1 Display Device

In the following example embodiments, ranges of display size,resolution, and refresh rate are determined that provide a naturalappearance of a visible portion of an eyeball on a flexible display bentinto horizontally curved surface that occupies space and consumes powerat a reasonable rate for the ocular prosthesis 110.

FIG. 9A and FIG. 9B are block diagrams that illustrate an exampledisplay device disposed in a housing having a form factor for an ocularprosthesis, according to an embodiment. According to the illustratedembodiment, the ocular prosthesis comprises a housing 901 with a formfactor suited for insertion in the prosthesis space behind the eyelidand anterior to the orbital implant. FIG. 9A is a block diagram thatillustrates an example vertical cross-section through the housing 901.The posterior surface 903 of the housing 901 has a posterior radius ofcurvature 905 of about 10 millimeters (mm, 1 mm=10⁻³ meters) around aposterior center 904. The anterior surface 906 of the housing 901 has ananterior radius of curvature 908 of about 13 mm around an anteriorcenter 907 displaced 3 mm forward of the posterior center 904. Thehousing 901 is vertically symmetric about a vertical symmetry axis 902.

In the vertical cross-section of FIG. 9A, the display device 910 is notcurved, is about 13 mm high, and is set back from the anterior surfaceof the housing 901 by a display setback 919 of about 0.5 mm. Thus thedisplay 910 has a display height 911 of about 13 mm. Combined with theother dimensions already cited, this places the display 910 about 3.68mm in front of the posterior surface 903, and the anterior surface 906about 6 mm in front of the anterior surface 903, along the verticalsymmetry axis 902. In order that the display 910 is visible at theanterior surface of the ocular prosthesis, at least a transparentportion 909 of the housing 901 is transparent to light. In someembodiments, one or more lenses are disposed in the transparent portion909 in order to give the appearance of curvature in the vertical. In thehorizontal cross-section of FIG. 9B along the vertical symmetry axis902, the display device 910 is curved, with a display radius ofcurvature 915 and a display center 914. The display length 912 is about26 mm. The display 910 is separated from the posterior surface 903 ofthe housing 901 by about 3.68 mm as depicted in FIG. 9A. Between thedisplay 910 and the anterior surface 906 of housing 901 is transparentportion 909 of housing 901. In some embodiments, the centers and radiiof curvature of the anterior surface 906 and the posterior surface 903in the horizontal cross-section are the same as in the verticalcross-section.

Both emissive and reflective displays can be fabricated with the sizeand shape of display 910, as described in more detail below. In variousembodiments, the display area of the ocular prosthesis for a normaladult ranges from about 24 mm length to about 26 mm length and fromabout 12 mm height to about 18 mm height. In various embodiments, arange of display areas of the ocular prosthesis for a child or smalladult is selected from a set that is about two thirds or more of thesize for a normal adult. In some embodiments, memory-in-pixel and an LCDover reflective backing layer is used to produce an excellent colordisplay with very low power while the display is static, yet capable ofvideo rate updates.

FIG. 9C is block diagram that illustrates an example image 920 forrendering on a display device 910, according to an embodiment. The imagehas an image length 922 that is greater than the display length 912, andan image height 921 that is greater than the display height 911. Forexample, in some embodiments, the image height 921 is twice the displayheight 911 and the image length 922 is twice the display length 912, sothe image area is quadruple the display area 913.

The image 920 is made up of a background 923 that represents the sclerawith one or more conjunctival blood vessels 924. The image 920 alsoincludes an iris 925 and a variable sized pupil 926 centered on imagecenter 927. Movement of an eye is represented by movement of the image920 relative to the display area 913. As the eye is to be displayedmoving up, the image 920 scrolls up relative to the display area 913,thus bringing the lower portions of the image 920 into the display area913 and moving a portion of the image 920 above the iris 925 off thedisplay area 913. The opposite occurs when the eye moves down.Similarly, as the eye is to be displayed moving left with respect to aperson looking at the subject, the image 920 scrolls left relative tothe display area 913, thus bringing the right portion of the image 920into the display area 913 and moving a portion of the image 920 left ofthe iris 925 off the display area 913. In some embodiments, the area ofimage 920 is the same as the display area 913; and, as a row or columnof pixels scrolls off one end of the display area 913, it appears alonga corresponding row or column, respectively, on the opposite side of thedisplay area 913. In some embodiments, the background is fixed andpixels that constitute the background are not moved as the eye isdisplayed to be moving. In these embodiments, only the iris 925 and thepupil 926 move across the display area 913.

FIG. 9D is a block diagram that illustrates an example image controlscreen 960 for controlling properties of the image and image changesover time to determine acceptable display properties, according to anembodiment. The screen includes one or more active areas that allow auser to input data to operate on data. As is well known, an active areais a portion of a display to which a user can point using a pointingdevice (such as a cursor and cursor movement device, or a touch screen)to cause an action to be initiated by the device that includes thedisplay. Well known forms of active areas are stand alone buttons, radiobuttons, check lists, pull down menus, scrolling lists, and text boxes,among others. Although areas, active areas, windows and tool bars aredepicted in FIG. 9D as integral blocks in a particular arrangement onparticular screen for purposes of illustration, in other embodiments,one or more screens, windows or active areas, or portions thereof, arearranged in a different order, are of different types, or one or moreare omitted, or additional areas are included or the user interfaces arechanged in some combination of ways.

In one portion of screen 960 is a representation of a display area 913of display 910, e.g., 13 mm high by 26 mm long. Active area 930 is apull down menu that allows selection of a frame refresh rate, e.g., 22frames per second as depicted in active area 930. Active area 932 allowsselection of contrast for the image presented in display area 913.Similarly, active area 934 allows selection of brightness for the imagepresented the display area 913; and, active area 936 allows selection ofresolution, in pixels per inch (PPI), for the image presented in thedisplay area 913. The example values of contrast brightness andresolution depicted in FIG. 9D are −3, −3 and 166, respectively, whichrepresents moderate contrast and brightness and high resolution. It isexpected that fewer pixels per inch will provide realisticrepresentations of a visible portion of an eyeball of a subject andprovide the advantage of fewer array elements, less power consumption,faster computations and better response.

Active area 938 allows selection of the number of bits used to representeach color at a pixel. The more bits used to represent a color at eachpixel, the more memory and processing time is required to generate theportion of the image on the display area 913. The example value of a16-bit bit depth allows a representation of 65,536 different colors andis expected to be greater than needed for realistic representations of avisible portion of an eyeball of a subject. Active area 940 is a buttonthat causes the display area 913 to present an eye that appears torotate to the viewer's left. Similarly, active area 942 is a button thatcauses the display area 913 to present an eye that appears to rotate tothe viewer's right. Active area 944 is a button that allows a user toload a file of recorded natural movement, which can be played in displayarea 913 with different settings for brightness resolution bit depthetc. so one can determine which settings produce a natural appearance.Active area 946 allows a user to manipulate the direction of the iris inthe display area 913 by moving a pointing device, such as a mouse.

Screen area 950 includes three buttons for controlling the display areaby clearing the image, turning off the display area or turning on thedisplay area, respectively. Screen area 952 includes two buttons forcontrolling which image is presented in the display area 913. One buttonallows a user to reset an image to its original orientation, and thesecond button allows a user to download a particular image from storage.

By operating the active elements of screen 960 in view of severalpractitioners, a range of image properties that provide acceptablynatural and realistic appearance and movement of an eye of a subject wasdetermined.

In an experimental embodiment, an active-matrix organic light-emittingdiode (AMOLED) development system was procured and a Windows applicationwas created to display a representative eye image on the display, asdepicted in FIG. 9D. Image procession algorithms were created in MATLAB™from MATHWORKS™ of Natlick, Mass. to render the image in the mostaccurate form and save it to a Joint Photographic Experts Group (JPEG)file. A MATLAB™ algorithm was also developed to create a real-time movieusing eye kinematic data supplied by the Memorial Sloan Kettering CancerCenter (MSKCC) of New York, N.Y. This program produced an Audio VideoInterleave (AVI) formatted movie file representing typical eye motionsthat may be encountered by the ocular prosthetic system in normal use.The movie was played back multiple times for the viewers while thedisplay parameters (refresh rate, color depth, contrast and resolution)were varied. The minimal parameter values that yielded aestheticallyacceptable (also called herein “realistic” or “natural”) results weredetermined by a subjective judging panel assembled by MSKCC. Thedemonstrator was presented at MSKCC where the visual output was judgedby Applicants as the display parameters were adjusted. Some generalconclusions are presented next.

Frame rate (how often the display is updated) was determined to beimportant. Applicants determined that the image quality improved withhigher frame rates, up to the 22 frames/second (FPS) limit of theexperimental display. However, fast movements (cycads) were determinedto look better at a lower frame rate whereas smooth movements (pursuits)improved at higher frame rates. The eye motion file used for thisdemonstration emphasized the cycad motions and selecting a lower framerate eliminated some of the more extreme jumps. Overall, 17 FPS wasjudged to be adequate, which corresponds to a refresh time of 59milliseconds (ms, 1 ms=10⁻³ seconds). Thus a display frame rate in arange from about 17 FPS (refresh time of about 59 ms) to about 22 FPS(refresh time of about 45 ms) is advantageous for natural appearance ofeye movements. In some embodiments, a refresh time of about 67 ms (aframe rate of about 15 FPS) is used. Similar results are expected forother display device types (electronic reflective and mechanical). Insome embodiments, 10 FPS is acceptable. Thus, in various embodiments aframe rate is selected in a range extending from about 10 FPS and aboveto about 22 FPS or more.

Resolution was also determined to be important. The AMOLED display had aresolution expressed as a dot pitch (reciprocal of pixel size) of 166pixels per inch (PPI), which proved more than adequate for a goodrendition of the image. Applicants determined resolution was adequatefor a natural appearance until the simulated pixel size was increased to50 PPI. Due to the way that this down-sampled image was created, theedges of the (larger) simulated pixels were softened, making a lessblocky appearance than a display having physically large pixels. Thus adisplay resolution in a range from about 50 PPI to about 166 PPI providea natural appearance of a visible portion of an eyeball of a subject. Amore advantageous range of resolutions extends from about 60 PPI toabout 80 PPI. Applicants have determined that a resolution of about 70PPI (pixel size of about 0.36 mm) is even more advantageous because itprovides an acceptable appearance and can be achieved with fewer pixels,which reduces complexity and power consumption over displays that havehigher resolution, e.g., 80 PPI to about 166 PPI. Similar results areexpected for other display device types (electronic reflective andmechanical).

At 70 PPI (pixel size of 0.36 mm), the 26 mm by 13 mm display areacomprises an array of about 72×36 pixels (about 2592 pixels). In someembodiments, to achieve the advantage of efficiency in addressing pixelelements using binary arithmetic, the display area comprises 64 by 32pixels (2048 pixels) for a display area of about 23 mm in length andabout 11.5 mm in height at 70 PPI, or the originally stated display areaof 26 mm by 13 mm with a resolution of about 62.5 PPI. Applicants alsodetermined that acceptable appearance is achieved with a display areathat is about 24 mm long and about 12 mm high. This smaller displayarea, used in some embodiments, offers the advantage of fewer componentsto realistically present an image of an eyeball of the subject orgreater resolution for a display area comprising 64×32 pixels. Thus, invarious embodiments, resolution is selected in a range extending fromabout 60 PPI and greater.

Unlike a reflective display (or the natural eye) the AMOLED displayemits light. It was difficult to adjust color and contrast of the AMOLEDdisplay for a lifelike appearance as the lighting conditions in the roomchanged. In dim light it was found to be difficult to prevent the eyefrom glowing, which yields a robotic appearance that is unpleasant andundesirable. Making the “white” of the sclera look natural requiredcareful adjustment of the color balance and this also varied with theroom light. Overall, it was felt that a reflective display would providea more natural image with less difficulty. Thus, Applicants determinedthat a reflective display device provides the advantage of morerealistic appearance with simpler computations under varying ambientlight conditions.

In various embodiments, display technologies include emissive displaydevices such as liquid crystal display (LCD) and AMOLED, and reflectivedisplay devices such as electro-phoretic (EP), electro-fluidic (EF) andelectro-wetting (EW). LCD display technology and manufacturing methodsare by far the most mature, but the multiple polarization and electrodelayers require fabrication on a rigid structure which makes thesedisplays thicker relative to the other less mature technologies. LCDsalso require a backlight which further adds to the overall thickness andpower requirements.

AMOLED display devices, used in the experimental embodiment describedabove, are a newer and less mature technology than LCDs. These displaysare commercially available on a limited basis in select sizes in newerproducts. AMOLEDs emit light and do not need a backlight or polarizationlayer like an LCD. This not only makes these displays thinner and lesspower hungry than LCDs, it also makes it possible to produce AMOLEDs ona flexible substrate, thus making this technology suitable for thedisplay 910. As described above, AMOLED displays share a commondisadvantage with LCD backlights, that is, the ambient light conditionwould desirably be monitored closely and the brightness of the displayadjusted so that it does not glow or appear to give off light. When thedevice battery becomes discharged, an AMOLED display will go darkresulting in an undesirable appearance.

Reflective electro-phoretic (EP) displays use charged colored pigmentparticles in a clear fluid medium to create images when these particlesare attracted or repelled by capacitive elements on the face andsubstrate of the display. The pixel takes on the color of the pigmentedparticles that are forced to the top (visible) surface.

Reflective electro-fluidic (EF) display devices use a variable volumemicro-electromechanical system (MEMS) chamber to draw-in or expel a dyedliquid medium to produce various shades of color. When the pixel chamberis expanded by electrostatic forces, the colored fluid flows into thevisible chamber and the pixel becomes the color of the dye. When thepixel chamber contracts, most of the fluid is expelled and the pixelapproximates the substrate color. The shade can be modulated by varyingthe volume of the chamber. In some embodiments, this is a two colorsystem—arbitrary combo of one fluid color and one substrate color—and isadequate for some uses. In other embodiments, more than one fluidchamber can be included in each pixel for additional color layers and afull color system.

Reflective electro-wetting (EW) display devices use a voltage to modifythe wetting properties of a solid material. A display using thisprinciple creates an optical switch by contracting a colored oil filmwith a voltage applied to an electrode in contact with it. As with EFdisplays, the colored region of a pixel can be modulated to producevarying shades of the color. More than one fluid chamber can be includedin each pixel.

These reflective displays are the newest and least mature displaytechnologies; however, improvements in device performance arecontinually and rapidly being achieved. At the time of this writing thecharacteristics of reflective displays include: 1) material selectionand fabrication methods are intrinsically linked; 2) at FUJIFILM™DIMATIX™ of Santa Clara, Calif., 0.047 mm features are possible with adrop volume of 10 picoLiter (pL, 1 pL=10⁻¹² Liters); 3) at DIMATIX™0.023 mm features are possible with a 1 pL drop; 4) at NANOMASTECHNOLOGIES™ of Vestal, N.Y., silver inks make possible 0.010 mmfeatures. With features this small, several colors can be combined ateach 0.360 mm pixel for full red-green-blue (RGB) orcyan-magenta-yellow-black (CMYK) spectrum of color combinations. Eachcolor can be expressed at any degree of precision, but typically in 16to 256 steps, using 4 bits to 8 bits, respectively, for each color.

In some embodiments, holographically formed polymer dispersed liquidcrystals (HPDLC) are used.

Color palette and bit depth ranges are advantageously kept as small aspossible to still provide realistic renderings of sclera, iris and pupilwhile reducing pixel circuitry complexity and computational loads.Clearly, a full color (CMYK) display (4×8 bits=32 bits) will satisfy thecolor gamut useful to reproduce a realistic eye image. But given thecomplexities of fabricating a flexible display and thin film transistor(TFT) backplane in the confined volume of this product, a significantadvantage may be achieved by limiting the color gamut of the displayused to produce a realistic rendering of the eye.

The color range of a typical eye can be an appreciable portion of thevisual spectrum. A typical human sclera has surface vascular structuresthat appear as random red lines that are concentrated toward theperipheral regions. Hues of yellow, beige and blue are also common inthe sclera thus giving the “white” of the eye a significant colorspectrum especially when added to very different iris colors. The irisand pupil tend to have a narrower color spectrum than the sclera and arereproduced to an acceptable level with a two color system, assuming thatthe two colors were chosen to be near the mean hues of these features,in some embodiments. Such two color systems can be expressed in aslittle as 2×4=8 bits or as much as 2×8=16 bits, depending on thegranularity of color changes supported.

A traditional prosthesis uses red threads to emulate the surfacevascular structures of the sclera. It was observed under a 20×microscope that these red threads actually continue for some distanceinto the iris. Even though the iris was a light shade of blue, thesethreads were not visible to an unaided eye. Applicants determined thatthe color gamut of the display device could be reduced if the visiblesclera and its fine red features were fabricated into the moldedprosthetic package. Thus in some embodiments, the sclera image would bethe background “color” of the display, apparent everywhere but in theregion of the iris and pupil. The iris and pupil are adequatelyrendered, in some embodiments, using just a two color scheme, thusgreatly reducing the complexity of the display, backplane and dataprocessing. In at least some such embodiments, the two base colors forthis two color display are specialized for a specific eye color group,for instance one pair of colors for rendering the iris of subjects withblue eyes and a second pair of colors for rendering the iris of subjectswith brown eyes. In these embodiments, the sclera features are static asthe iris and pupil image moves about the display area. It is anticipatedthat the effects of this will not be noticeable in normal use; and,thus, that the display will appear natural. In some such embodiments,displays incorporating different pigments are inventoried to createprostheses covering the wide range of individual eye coloration. Somedegree of customization of the sclera background is also performed insome embodiments. Thus, in various embodiments, the color palette bitdepth is selected in a range from about 8 bits to about 32 bits. In someembodiments, 16 bits are arranged as 5-5-6 for each of three colors,which provides a color depth of at least 5, a reasonably good colorimage if the palette is adjusted properly.

In some embodiments, creating a realistic eye image includes properlyrepresenting the changes which occur during pupil dilation/contraction.If the pupil were represented as a simple black dot that occludes eithermore or less of a fixed iris pattern, the result isn't very realistic asambient light changes. This is because there are visible changes in thestructure of the iris as the pupil changes size. In some embodiments, amuch more realistic display is obtained using a physiologically accurateimage of the eye for a range of possible dilation of the pupil. Analgorithm is applied in some embodiments to smoothly transition from oneimage to another, e.g., using morphing techniques widely known in theart. This image is translated in response to position sensor informationso that the eye appears to be gazing in the correct direction.

The reflective EP, EF and EW display devices share commoncharacteristics and have significant advantages over AMOLED displaydevices. EP/EF/EW display device power usage is each lower than emissivedisplay devices because power is consumed only when pixels are changingstate. In contrast, for example, power in each AMOLED pixel iscontinually consumed while an image is presented. EP/EF/EW displaydevices are reflective display devices and do not emit light so ambientlight sensing and complex corrections are not required to keep suchdisplay devices from appearing to glow under low light conditions.EP/EF/EW display device images are persistent and do not change afterpower is removed. This allows the display to have the appearance of atraditional eye prosthesis after battery discharge or device electronicfailure. This makes a confidence alarm that issues when power reaches acritically low level less desirable for such displays and also makescarrying a back-up traditional prosthesis less desirable.

In some embodiments, degraded performance or failure of one or morecomponents of the ocular prosthesis causes the subject to be alerted bya confidence alarm. For example, when power is about to be depleted foran emissive display device, the confidence alarm alerts the wearer whenthe battery has discharged to a predetermined level. Embodiments that donot employee a confidence alarm offer the advantage of removing theadded size, power and complex computational load of the confidencealarm.

Whichever display technology is employed in various embodiments, it isadvantageous that the display elements are fabricated on a flexiblesubstrate so that the display can be fabricated flat using standardprocess and then curved onto a cylinder about a vertical axis. This willfit it to the curve of the eye (horizontally at least) while avoidingcrinkling problems. It is noted that flexible is not stretchable, soconforming to a doubly curved surface (portion of a sphere) presentschallenges to avoid display damage. Thus a cylindrical curved display isadvantageous over a spherically curved display. PLASTIC LOGIC™ ofCambridge, United Kingdom fabricates flexible printable electronics. Inan example method for assembling the display device, a display medium insheet form is purchased from a manufacturer of a reflective display,such as a color electronic ink medium from E INK™ Corporation ofCambridge, Mass. (used in the well known KINDLE™ reader from AMAZON™ USAof Seattle, Wash.) and mated to a flexible TFT backplane from aprintable electronics fabrication facility, such as E3 DISPLAYS ofPhoenix, Ariz.

Thus, in some embodiments, the display device is built on a flat,flexible substrate. As shown in FIG. 9A, Applicants have determined thatthere is sufficient internal volume to accommodate the display 910 withadequate room left over for the electronics (including communicationsmodule, processor and memory) and battery and sensor systems (includingthe implant detector and, in some embodiments, an ambient light sensor).

2.2 Power Source

Simulations were performed to determine the power demands of the displaydevice and other systems disposed in the ocular prosthesis. It was thendetermined that the power demand could be satisfactorily met with apower source, including battery, that fits within the housing 901 forthe ocular prosthesis. In some embodiments, a supercapacitor is used,even though the energy storage density (by volume) of the supercapacitorpresently is much lower than for a lithium cell.

Applicants were able to extrapolate an electrical model for a displaypixel and the associated TFT backplane, which is believed to beconservative. A usage model has been developed that approximates thenumber of pixel transitions over a given time. The switching speed ofthe display (refresh rate) is dependent on the drive voltage andconsequently, the power consumed. For the display device modeled, thereare 3380 addressable pixels and a refresh rate of 20 FPS (more than the2592 pixels in a 26 mm by 13 mm display area at 70 PPI resolution and 17FPS of an example embodiment, described above, capable of presenting animage of an eye with a natural appearance) and the sclera is representedby a fixed background.

A typical 12 mm diameter iris is comprised of approximately 1130 pixels.If the iris image were to move from one area of the display to a totallydifferent area in a single frame, there would be a change of 2×1130=2260pixels. A more reasonable estimate is about 20% of this number, e.g.,about 452 pixels per frame. At 20 frames per second, the total activityis about 20×452=9040 pixels per second.

Each pixel is effectively modeled as a capacitor. Each pixel isapproximated as a parallel plate capacitor with an area (A) of (320μm)²=1.024×10⁻⁷ m², a plate separation (D) of 30 μm and a relativepermittivity (∈r, also called a “dielectric constant”) of a medium valueof 80. The plate area is fixed by the size of the pixels. Plateseparation is estimated and the dielectric constant for water is used,which is an extremely high dielectric liquid. Capacitance, C, is givenby Equation 1.

C=∈A/D=∈r∈0A/D  (1)

Where ∈ is specific permittivity and ∈0 is permittivity of free space,equal to 8.85×10⁻¹² Farads per meter. Thus the capacitance per pixel is2.4 picoFarads (pF, 1 pF=10⁻¹² Farads). The energy, E, used to charge acapacitor is given by Equation 2 in Watts per second (Joules) based onthe voltage difference V between the two conducting plates of thecapacitor.

E=V ² C/2  (2)

The display drive voltage is proportional to the desired frame rate. Amanufacturer of electro-wetting (EW) display devices has characterizedtheir technology as having a 20 V drive voltage. It is estimated that adrive voltage at the pixel electrode of 10 V might be a bettercompromise between backplane transistor size, power consumption anddisplay update time. The power calculations were performed for threesets of assumptions to show that power consumption is extremely low foreven worst case conditions of drive voltage and capacitance. For V=drivevoltage of 10 V, Equation 2 yields 120×10⁻¹² Joules per pixel. The powerP is energy per unit time, t, and given by Equation 3.

P=E/t=E×U  (3)

where U is the usage in pixels per unit time. For the usage model of9040 pixels per second, the total display power is 1.08 microWatts (μW,1 μW=10⁻⁶ Watts). For V=drive voltage of 20 V, the total display poweris 4.34 μW. For a worst case with quadruple the capacitance to 10 pF, 20V driving voltage, and changing every pixel on every frame, the totaldisplay power is 135 μW.

In addition to the power consumed to change pixels, there is the powerconsumed by the backplane. The thin film transistor (TFT) backplane isthe active circuitry that supplies power to the pixels to change theiroperating state. The operating model presented here is simplified butrepresents a conservative estimate of the TFT backplane powerrequirements. Assuming the backplane involves 3 transistors per pixel toachieve full color (fewer transistors are used for a two color system asproposed for some embodiments), the total number of TFTs for the 3380pixels is 10,140. For a TFT backplane of conventional design, each ofthese transistors is driven (transitioned) once per frame, even if thedisplay content is unchanged. It turns out that this constitutes thedominant power sink for the display. For an update rate of 20 FPS, thecircuit load is 202,880 transitions per second. Each TFT is estimated tohave at most 5 pF gate-to-source capacitance. Driving this capacitanceconstitutes the primary energy dissipation factor in the backplane. Thegate drive voltage is typically 5 V higher than the pixel voltage. For a20 V pixel, the backplane energy per pixel is 1563×10⁻¹² Joules pertransition. Therefore, the total backplane power consumption is 317 μW.For a 10 V pixel, the backplane power consumption is only 79 μW.

The total power consumption for the display and backplane is given inthe table of FIG. 10A for several embodiments. FIG. 10A is a table thatillustrates example power consumption for an electronic display devicesuitable for an ocular prosthesis, according to various embodiments. InFIG. 10A, the display devices' assumed properties for each embodimentare given in column 1012 a. In this column, pixel is further abbreviatedto “pel.” Row 1014 a is for an embodiment with 10 V driving voltage perpixel, and 20% of pixels updated each frame, and three TFTs per pixel.Row 1014 b is for an embodiment with 20 V driving voltage per pixel, and20% of pixels updated each frame, and three TFTs per pixel. Row 1014 cis for an embodiment with 20 V driving voltage per pixel, and 100% ofpixels updated each frame, and three TFTs per pixel. Column 1012 b liststhe display plane power consumption for each embodiment. Column 1012 clists the backplane power consumption for each embodiment, which faroutweighs the display plane power consumption. Column 1012 d lists thetotal display device power consumption for each embodiment. The valuesin microWatts are as recited above.

Given the power consumption rates of the example embodiments of thedisplay device, the adequacy of storage battery properties appropriateto fit in the housing 901 of the ocular prosthesis can be evaluated.Several batteries with appropriate specifications are known to becommercially available. For example, at SOLICORE™ of Lakeland, Fla.,lithium polymer batteries about 0.45 mm in size provide 100 microAmperes(μA, 1 μA=10⁻⁶ Amperes of current) at 3.0 Volts. In an illustratedembodiment, a 3.7V and 25 milliAmperes (mA, 1 mA=10⁻³ Amperes ofcurrent) hours (mAHr) rechargeable battery cell with dimension of 10.8mm×19.0 mm×2.4 mm available from TENERGY CORP.™ of Fremont, Calif. andfound on All-Battery website as part number 241019 is used, which wouldfit into the available volume of housing 901. Based on this battery, theavailable energy is 333 Joules. The amount of time this battery cansupply power for the example embodiment of 10 V display and backplanewith 20% change per frame is 333 joules/80 μW, which is equal to about48 days. Even for the worst case, of 452 mW consumption, this batterylasts 205 hours (about 8.5 days). This leaves most of the power forother components of the ocular prosthesis during a daily wear andrecharge cycle. For a 16-hour wear duration, the example displayconsumes only 1.4% of the available power; and, the worst case displayconsumes only 7.8% of the available power.

An additional component consuming power available for the display is aconverter to up-convert the 3.7 V of the battery to the 10V or more(e.g., up to 25 V) for the display device. An efficient power conversioncircuit would yield about 95% efficiency whereas a relatively wastefuldesign would yield only 80% efficiency. In either case, a good operatinglife is still retained for the example embodiments of the displaydevice. Most other circuits in the ocular prosthesis will be able to rundirectly from the battery voltage.

Lithium polymer batteries have a desirable combination ofcharacteristics for the ocular prosthesis with display device. Thesecharacteristics include: best power to weight and power to size ratio;capable of being fabricated into non-standard shapes; capable of beingfabricated as flexible; low self discharge rate; and no memory effect.Battery manufacturers specify a wide range for the number of usefulcycles that a battery can be charged and discharged, from a low of acouple hundred cycles to over 10,000. This is likely due to the factthat there is no standard for calculating this number which is highlydependent on the discharge state of the battery, temperature, and thedefinition of useful life. When a lithium polymer battery is new, it iscapable of being recharged back to its rated capacity but, the morecharging cycles a battery endures, the lower it's charging capacitybecomes. So the question of battery life for a particular application isbetter defined in terms of acceptable continuous wearable time for thattime.

FIG. 10B is a graph that illustrates example recharge power for abattery suitable for an ocular prosthesis, according to an embodiment.The horizontal axis 1002 is number of recharge cycles and the verticalaxis 1004 is percent of initial power capacity. Trace 1006 indicatesthat as the number of discharge and recharge cycles increase, thecapacity of the battery diminishes. However, even after 500 cycles, thebattery is still able to provide over 85% of its initial capacity. It isexpected that with normal use, the battery lifetime will be in excess of3 years, with 5 years (about 2000 cycles) as a sensible goal. For anembodiment using a battery with a (nominally) 3.7V unit rated at 25 mAHr available from TENERGY CORP.™ of Fremont, Calif. and found onAll-Battery website as part number 241019, and a 16-hour dailyendurance, maximum power consumption of approximately 5 mW (equivalentcurrent consumption is about 1.5 mA) should still be available after2000 cycles.

Various voltages are used for the different functional blocks. The usedvoltages are expected to range, in various embodiments, from 1.0 V to5.0 V for the electronics and up to 25 V for the TFT backplane anddisplay. The voltage available from the battery itself may vary from 4.2V to 2.5 V depending on the state of discharge. Therefore, powerconversion circuitry is employed, in some embodiments, to convert andregulate the available battery power to meet the uses of the varioussystem subcomponents. Circuit design and components that meet thesespecifications are well known and readily available, being used indiverse products such as cell phones, watch backlights and personal dataassistants (PDAs). The art in implementing this functional blockincludes the mitigation of electrical noise coupled into the processorand display due to the close confines of the prosthesis housing 901.

From the standpoint of energy density, the obvious choice is a lithiumchemistry. However, printable batteries are emerging that are based onother chemistries such as zinc. These batteries are less energyefficient than lithium, but the ability to print (shape) the battery tobest utilize available space might yet make this approach the winner. Ifan absolute voltage reference is utilized in some embodiments, in orderto effectively recharge the battery, a tiny primary cell that has a longshelf life and stable output voltage is included. In some embodiments asemiconductor reference is used instead of, or in addition to, theprimary cell; but such semiconductor references are large and consumerelatively more power.

2.3 Implant Markers and Detectors

In some embodiments, the position and movement of the iris 925 and pupil926 in the display area 913 on the display device 311 is based on theorientation and movement of the orbital implant 120. In some of theseembodiments, an implant detector comprises a plurality of sensorsdistributed in the housing 901 of the ocular prosthesis 110 totriangulate on the position of a marker 122 that moves with the orbitalimplant 120. In four embodiments described in this section, a magneticmarker is used with Hall Effect sensors, a non-magnetic conducting foilis used as a marker with capacitors, a conductor is used as a markerwith inductance sensors, and a light emitting marker is used withphotodiodes.

2.3.1 Hall Effect Implant Detectors

FIG. 11A through FIG. 11D are block diagrams that illustrate exampledetection of a magnet moving with the orbital implant using Hall effectsensors on the ocular prosthesis, according to an embodiment. FIG. 11Ais a block diagram that illustrates an anterior portion of the orbitalimplant 1100 with a magnet 1102 configured to move with the orbitalimplant 1100. In some embodiments, the magnet 1120 is inserted in a holedrilled into the orbital implant 1100. In some embodiments, the magnetis attached to the conjunctiva to move with the orbital implant, such asdescribed below with reference to FIG. 11E and FIG. 11F or FIG. 11Gthrough FIG. 11J.

FIG. 11B is a block diagram that illustrates an anterior view of anocular prosthesis 1110 with example locations indicated where aredisposed, at some depth behind or beside the display device, four Halleffect sensors 1120 a, 1120 b, 1120 c, 1120 d (collectively referencedhereinafter as Hall effect sensors 1120) that are able to detect amoving magnetic field when in the vicinity of the magnet 1102. Thismethod of determining eye position relies on measuring the magneticfield strength of the implanted magnet 1102 at three or more points andthereby triangulating the position of the magnet. Considering that thefield strength of a magnetic dipole falls off roughly as the cube ofdistance, the four sensors 1120 are arranged to minimize the distanceany Hall Effect sensors would be from the magnet. In other embodiments,more or fewer Hall Effect sensors 1120 are used.

FIG. 11C shows the anterior view of the ocular prosthesis of FIG. 11Bwith position 1104 a of the magnet behind the ocular prosthesisindicated by a dashed circle. Three zones are created, by the four HallEffect sensors 1120 taken three at a time, indicated by sections 1122 a,section 1122 b and section 1122 c (collectively referenced hereinafteras Hall Effect sections 1122). As the magnet moves around, a processexecuting on the processor 301 determines which zone the magnet is in byusing the 3 strongest measurements of the Hall Effect. Within a zone,the distance to the magnet from each sensor is determined by thestrength of the Hall Effect, and the position of the magnet within thezone is determined by triangulating the distance from the three closestsensors. For example, when the implant has moved to the viewer's leftand up, the magnet is in section 1122 a, as depicted in FIG. 11D. FIG.11D shows the anterior view of the ocular prosthesis of FIG. 11B withnew position 1104 b of the magnet behind the ocular prosthesis. The HallEffect measurement is greatest for Hall Effect sensors 1120 a, 1120 band 1120 c, therefore the magnet is in Hall Effect section 1122 a. TheHall Effect is greatest at sensor 1120 a, second greatest at sensor 1120c and third greatest at sensor 1120 b, indicating increasing distancesfrom each sensor. The processor 301 determines the position 1104 b basedon these measurements.

A significant factor, in determining sensitivity of the measurement withdistance, is the strength of the attached magnet. For the size of magnetsuitable for attaching to the implant or conjunctiva, it appears that afield strength of 2500 gauss is practical in some embodiments. Invarious embodiments a field strength of half to twice this values isalso acceptable. A reasonable goal is for the sensitivity of the HallEffect measurement to equal the resolution of the display device, e.g.,the size of a pixel, about 0.36 mm. While it is envisioned that acylindrical magnet with the poles oriented facing out and back will beused in some embodiments, in other embodiments other configurations areused.

FIG. 11E through FIG. 11J are block diagrams that illustrate an examplemarker configured to be attached to the conjunctiva that moves with theorbital implant, according to various embodiments. As shown in a sideview in FIG. 11E and a perpendicular view in FIG. 11F, a marker 1140,such as the magnet 1102, is inserted into a small tube 1130 less thanabout 1 mm in diameter. One end of the tube is compressed, either beforeor after insertion of the marker 1140, to form a compressed end 1131that prevents passage of the marker through that end. Any method may beused to form the compressed end 1131, including crimping, gluing,stapling, or suturing, or some combination. After insertion of themarker 1140, the remaining end of the tube is compressed, as indicatedby the dashed lines. The tube with both ends compressed and markerenclosed is then fixed with or without sutures to the conjunctiva overthe orbital implant to move with the orbital implant, either exactly orin some related manner. This arrangement and method offers the advantageof being suitable for retrofitting an orbital implant formerly insertedinto the eye socket 12 and surgically attached to the eye muscles 18.

A disadvantage of the implanted magnet as a marker is that it interfereswith nuclear magnetic resonance (NMR) imaging (MRI) and equipment, whichis a commonly used diagnostic tool that is desirably not off limits to asubject using the present ocular prosthesis. To address the issue of MRIexposure, the magnet could be arranged to be removable without asurgical procedure. One such arrangement is to affix a non-metalliccontainer, such as the tube 1130 described above, into the conjunctivain a way not to interfere with either the sphere or the ocularprosthesis, but open to the surface. A magnet is placed into thecontainer and held in place by some method, such as friction, sutures ora clip. It is expected that a tool, which may be specially designed forthis purpose, will be used for insertion and extraction of the magnetfrom the container.

It is anticipated that the magnetic sensor will be immune to mostsources of man-made interference since there are relatively fewelectronic devices that emit strong magnetic fields. Furthermore, if asmall magnetic field were to be emitted, say from a cell phone, it wouldbe radiating in the GHz frequency range (its operating frequency) whichis far from the nearly dc frequency the Hall Effect implant detectoruses.

Power dissipation for operating the Hall Effect sensors is expected tobe comparable to the display described above and processor, describedbelow. Considering that a measurement is made once per frame (50 ms at20 FPS) and it is expected that a measurement should take no more than 1ms, the illustrated Hall Effect-sensors will only be operating 2% ofthe-time. For the Hall-Effect devices that have been identified, partnumbers #A1391, A1392, A1393, A1395 from ALLEGRO MICROSYSTEMS INC.™ ofWorcester, Mass., the current consumption is computed to be less than 10mA when operating, and therefore the sensor will have an average currentconsumption of only 2% of that, or around 200 μA. This is about 15% ofthe power budget when operating directly from the battery.

In some embodiments, a paddle marker is configured to hold a magnet orsome other emitter or detectable device for use in detecting motion ofthe orbital implant, and any associated electronics. FIG. 11G depictsdistal plan view of a paddle marker 1150 with an detectable device 1154centrally located and six circular indentations 1152 a. 1152 b, 1152 c,1152 d, 1152 e, 1152 f (collectively referenced hereinafter asfenestrations 1152), set three at a time in each blade (broad) portionof paddle marker 1150. These fenestrations 1152 are configured to allowconjunctiva tissue fixation through the holes to stabilize the paddle onthe implant and prevent migration relative to the orbital implant. Thepaddle marker is implanted under the conjunctiva to the orbital implantand is not connected with other parts of the prosthetic device. Thepaddle marker contains within it the magnet or other emitting ordetectable device and is placed in position surgically or with asub-conjunctival injector or delivery device. For example, circularfenestrations 1152, 1152 b and 1152 c are found in broad portion A ofmarker 1150. Broad portion A makes up one blade of the paddle marker1150.

The dimensions of the paddle marker are small enough so that the entiremarker sits easily in front of the orbital implant. For example thenarrow shaft connecting the blades is less than 0.1 inch (2.4 mm) wide.In the illustrated embodiment, the shaft is about 0.04 inches (0.9 mm)wide. FIG. 11H shows a side elevation view of the marker 1150 that isalso preferably less that 0.1 inch (0.6 mm). In the illustratedembodiment the marker is about 0.04 inches (1.0 mm) at its widest in theshaft and narrows to about half that thickness in each blade portion ofthe marker 1150. FIG. 11I depicts close up of a blade, broad portion A,with example dimensions, such as circular indentation diameter of about0.035 inches. Based on a coordinate system with origin at the center ofthe middle indentation 1152 b, the widest portion of the blade extendsabout 1 millimeter above and below the origin, and the end of the markeris about 2.3 mm from the origin, and the two remaining indentations inthe portion A are centered 1.1 mm left and right of the origin. FIG. 11Jdepicts a perspective view of the marker 1150 with indentations 1152 anddetectable device 1154.

2.3.2 Capacitance Implant Detectors

The capacitive sensor is based on a variable capacitor principle. Acircular conducting foil is implanted into the conjunctiva. Additionalfoils inside the prosthesis act to form simple serial plate capacitors.As these surfaces move with respect to one another, the overlappingareas change and so does the capacitance. This effect is easily seenfrom the defining equation of capacitance illustrated in FIG. 12Athrough FIG. 12 D. FIG. 12A through FIG. 12D are block diagrams thatillustrate example detection of the orientation the orbital implant withsensors on the ocular prosthesis that measure variable capacitance,according to an embodiment. FIG. 12A is a block diagram that illustratesan anterior portion of the orbital implant 1200 with a non-magneticelectrically conducting implant foil 1202 configured to move with theorbital implant 1200. In some embodiments, the foil 1202 is inserted ina conjunctiva covering the orbital implant 1200.

FIG. 12B is a block diagram that illustrates an anterior view of anocular prosthesis 1210 with example locations indicated where aredisposed, at some depth behind or beside the display device, fourconducting foils 1212 a, 1212 b, 1212 c, 1212 d (collectively referencedhereinafter as prosthesis foils 1212) that are able to form serialcapacitors when in the vicinity of the implant foil 1202. This method ofdetermining eye position relies on measuring the capacitance at three ormore capacitors and thereby triangulating the position of the implantfoil 1202. The circular central fixed foil is used to drive the largercircular foil on the moving surface. The geometric constraint is thatthe driving foil advantageously overlaps the driven foil completely forall motions of the eye. This keeps the driving signal to the moving foilconstant. The capacitance between the moving foil and the three annularsense foils are measured. The ratio of these capacitances is used todetermine position. This is considered series capacitance because thedrive is first capacitively coupled to the moving foil, thencapacitively coupled a second time back to the three fixed sense foils.In other embodiments, more or fewer prosthesis foils 1212 are used.

FIG. 12C shows the anterior view of the ocular prosthesis of FIG. 12Bwith position 1220 a of the implant foil 1202 behind the ocularprosthesis indicated by a dashed circle. Four capacitors are created. Asthe implant foil 1202 moves around, a process executing on the processor301 determines where the implant foil is centered using the 3measurements of capacitance at the 3 peripheral foils. The coverage ofthe implant foil 1202 by each prosthesis foil 1212 is determined by thestrength of the capacitance, and the position of the implant foil 1202is determined by triangulating the coverage from the three peripheralfoils.

Locating the foil in the conjunctiva instead of on the implanted sphereaddresses two important issues. First, the vestigial motion of thesphere is actually driven by the motion of the conjunctiva. For a newlyimplanted sphere, it takes time for the conjunctiva to integrate withthe sphere. Until this integration takes place, the sphere is free tomove, resulting in an arbitrary final position of any attached foils.The second advantage is for patients who have had a prosthetic eye forquite some time. For these patients, performing a small procedure on theconjunctiva is favored over implanting a new sphere.

Depending on how the implant foil 1202 is surgically installed, there isa possibility that the foil 1202 could move and rotate before becomingintegrated with the skin. To accommodate this motion, a single circularfoil is placed somewhat centered as shown in FIG. 12A. This constructioncompletely resolves the issue of rotation and it is believed that theexact placement is not critical. Desirable properties for the foilmaterial are non-magnetic for compatibility with MRI equipment,electrically conductive, biologically inert and flexible. Theconstruction of the implanted foil also needs to consider eddy currents,which will cause heating, when exposed to the strong RF magnetic fieldsof the MRI scanner. This issue is addressed in some embodiments by thecombination of providing slots in the foil and using a marginallyconductive material that will provide resistance to these circulatingcurrents.

Referring to FIG. 12B, the prosthetic center circular foil 1212 a staysessentially completely over the implanted circular foil 1202, creating afixed capacitor. The remaining three prosthetic foil pieces, 1212 b,1212 c and 1212 d each form a variable capacitor depending on theposition of the eye. It some embodiments, the computation of position isdone as a relative measure of the 3 variable capacitances. This methodreduces the effects of changing environmental conditions that will alterthe absolute capacitance values which can be normalized by the value ofthe fixed capacitor formed by the center coil 121 a and the implant foil1202.

While the measurement technique is based on the ratio of the 3 variablecapacitors, seemingly making the absolute capacitor valuesuninteresting, there are some practical aspects to be considered. FIG.12E and FIG. 12F are block diagrams that illustrate example factors thataffect the measured variable capacitance, according to an embodiment.The variables that mostly determine capacitance are the overlapping areaof the two plates 1232 (given by length 1235, L, times width 1233, W),the distance 1237, D, separating the two plates and the dielectricconstant of the material 1236 filling the space between the two plates.These properties describe capacitor 1230. The “textbook” formula thatdescribes the capacitor 1230, shown in FIG. 12E, is simplified as itdoes not include fringing fields 1242 of the electric field lines 1240illustrated in FIG. 12F. This simplification is valid when the aspectratio of the overlapping space dimension 1234, L, is larger than theseparating space 1237, D.

The capacitance C (in Farads) is given by Equation 1. The largestunknown for computing this capacitance is the dielectric constant, sincethe dielectric medium is the conjunctiva. According to published papers,the dielectric constant of human skin is dependent on a number offactors, including frequency. Considering that 70% of skin is composedof water which has a dielectric constant of only 80, then computing thetotal available capacitance across the surface of the eye, 20 mmdiameter, with a 1 mm separation for the thickness of the conjunctiva,is about 70 pF. If the total area were to be evenly divided among the 4prosthetic foils, each piece would measure one quarter of the total or17.5 pF. The variable capacitors would then expect to see a capacitancerange from around 1 pF to about 17.5 pF. The variable capacitors are inseries with the fixed capacitor of 17.5 pF creating a circuitcapacitance range of 0.9 pF to 8.75 pF. At these low values, straycapacitances in the driving and receiving circuitry could contaminate orobscure the measurement. In some embodiments, the effect of straycapacitances is compensated through a calibration procedure. Experimentswere performed that confirmed for the frequencies of interest (low MHzrange) the saline solution behaves substantially like pure water.

The variable conductivity of skin, which is highly dependent on moistureand salt (ion) content poses a considerable challenge. As previouslymentioned, the conductivity of the skin has an impedance that competeswith the capacitive reactance at the near 20 Hertz (Hz, 1 Hz=1 cycle persecond) frequency of interest. In effect this places a resistor inparallel with the capacitor, which attenuates the capacitive effect. Insome embodiments, a sinusoidal excitation around 100 kHz is used and theresulting signal measured at the processor 301. Providing a 10-to-1oversampling and averaging many 100 kHz cycles together allow bothamplitude and phase to be measured. In some embodiments, this approachis replaced with a more complicated experiment which measures theresonant frequency of an inductive/capacitive circuit. For thismeasurement, an inductor is placed in series with the foils to form aresonant tank circuit; and, when excited, exhibits the resonantfrequency.

Since all electronic devices emit electric fields, the capacitive sensoris inherently more susceptible to its environment than the magneticsensor. The amount of energy emitted from an electronic device is aknown quantity which can be used to help quantify this issue. In someembodiments, filters and shielding are included to address externalsources of electrical interference.

To maintain the lowest possible power consumption, it is desirable toprevent direct current (DC) from flowing through the conductive skindielectric. To accomplish this, the foils are advantageously coveredwith an insulating material. The total power consumption is mostlydependent on the impedance of the sensor's capacitors (which depends onthe dielectric constant of the skin) and on the percent of time it needsto run. As with the magnetic sensor, it's expected that this sensor willrun about 2% of the time, making the average power consumption less thanthe display.

2.3.3 Inductance Implant Detectors

The inductance sensor is based on principles of the de-tuning effects ofnearby conductors on LC circuits. An LC circuit, also called a resonantcircuit, tank circuit, or tuned circuit, consists of two electroniccomponents connected together; an inductor, represented by the letter L,and a capacitor, represented by the letter C. The circuit can act as anelectrical resonator, an electrical analogue of a tuning fork, storingenergy oscillating at the circuit's resonant frequency. The inductancesensor presented here offers an advantage over the Hall Effect sensorsin that this inductance circuit does not interfere with magneticresonance based medical imagers, such as MRI and MRSI. FIG. 12G throughFIG. 12L are block diagrams that illustrate example detection of aconductor moving with the orbital implant using inductance sensors onthe ocular prosthesis, according to an embodiment.

FIG. 12G is a block diagram that illustrates an anterior portion of theorbital implant 1250 with a conductor 1252 configured to move with theorbital implant 1250. In some embodiments, the conductor 1252 isattached to the orbital implant 1250. In some embodiments, the conductor1252 is attached to the conjunctiva to move with the orbital implant,such as described above with reference to FIG. 11E and FIG. 11F or FIG.11G through FIG. 11J.

FIG. 12H is a block diagram that illustrates an anterior view of anocular prosthesis 1260 with example locations indicated where aredisposed, at some depth behind or beside the display device, fourinductance sensors 1270 a, 1270 b, 1270 c, 1270 d (collectivelyreferenced hereinafter as inductance sensors 1270). This method ofdetermining eye position relies on measuring the distance from three ormore points and thereby triangulating the position of the marker. Inother embodiments, more or fewer inductance sensors 1270 are used.

FIG. 12I shows the anterior view of the ocular prosthesis of FIG. 12Hwith position 1254 a of the conductor behind the ocular prosthesisindicated by a dashed square. Three zones are created, by the fourinductance sensors 1270 taken three at a time, indicated by sections1272 a, section 1272 b and section 1272 c (collectively referencedhereinafter as inductance sections 1272). As the conductor 1252 movesaround, a process executing on the processor 301 determines which zonethe conductor is in by using the 3 strongest measurements of theinductance. Within a zone, the distance to the conductor from eachsensor is determined by the Equations 4a and 4b given below, and theposition of the conductor within the zone is determined by triangulatingthe distance from the three closest sensors. For example, when theimplant has moved to the viewer's left and up, the conductor is insection 1272 a, as depicted in FIG. 12I. FIG. 12J shows the anteriorview of the ocular prosthesis of FIG. 12H with new position 1254 b ofthe conductor behind the ocular prosthesis. The inductance measurementis greatest for inductance sensors 1270 a, 1270 b and 1270 c, thereforethe conductor is in section 1272 a. The processor 301 determines theposition 1254 b based on the distance measurements at these threesensors.

An example inductance sensor 1270, according to one embodiment, isdepicted in FIG. 12K, and comprises a tank circuit between terminals1276. The tank circuit includes sensor inductor Ls 1273 that compriseshalf of an open transformer, sensor resister Rs 1274, and sensorcapacitor C 1275. As depicted in FIG. 12L, in the presence of aconductor, e.g., target metal surface 1252, the fields radiating forminductor L 1273 induce eddy currents in the conductor depending on theconductance 1253 of the metal, setting up fields that oppose those ofinductor L 1273. The result is an equivalent circuit that resonatesaccording to combined inductance and resistance of the sensor and theconductor (e.g., metal surface 1252). The effect of the conductor 1252on the inductance of the equivalent circuit is given by L and depends onthe distance d 1255 between the inductor Ls and the conductor 1252, so Lis a function of d and represented as L(d). The energy drain to powerthe eddy currents appears as an additional resistance R, also a functionof distance d 1255, and represented as R(d). Thus the equivalent circuitin the presence of a conductor appears to have inductance 1283 ofLS+L(d) and resistance 1284 of Rs+R(d). The equivalent circuit has adifferent resonant frequency, which can be measured across terminals1276.

The resonant frequency f₀ of the equivalent circuit depends on theinductance L and capacitance C of the equivalent circuit, as given byEquation 4a.

f ₀=½π(LC)^(1/2)  (4a)

The equivalent parallel resonance impedance, Zp, is given by Equation 4b

Zp(d)=(1/([Rs+R(d)])*((Ls+L(d)])/C  (4b)

By measuring simultaneously the resonant frequency f₀ and the powerconsumed at the resonant frequency, the distance d can be determined.The resonance frequency gives L=Ls+L(d) using equation 4a; and the powerdepends on Zp which is used to derive d based on Equation 4b.

Example inductance sensors include the LDC1000™ inductance-to-digitalconverter from Texas Instruments™ of Dallas, Tex., which provides asensitive and versatile position-sensing technology. The LDC1000™measures the equivalent parallel resonance impedance Zp given byEquation 4b. The LDC1000 regulates the oscillation amplitude to aconstant level while monitoring the energy dissipated by the resonator.By monitoring the amount of power injected into the resonator, itcalculates the value of Zp. Also, measuring the oscillation frequency ofthe LC tank circuit determines the inductance of the helical coil in theLC circuit. Zp and frequency are output as digital values. Calibrated toread out changes in the coil's inductance to 24-bit precision, theLDC1000 drives and monitors the tank circuit 1270. The drive frequency,which determines the dimensions of the coil to some extent, can beanywhere from 5 kiloHertz (kHz, 1 kHz=10³ Hertz, Hz, 1 Hz=1 cycle persecond) to 5 MegaHertz (MHz, 1 MHz=10⁶ Hz). In addition to providing foroscillation frequencies from 5 kHz to 5 MHz, the value of Zp cantheoretically range from 798 Ohms (Ω) to 3.93 MegaOhms (MΩ, 1 MΩ=10⁶Ohms). In practice, a circuit designer selects from a tighter range andenters those values in a pair of registers.

2.3.4 Optical Implant Detectors

In some embodiments, tracking the position of the conjunctiva isperformed by disposing an imager on the curved posterior surface of theocular prosthesis. The pixel density of the display device(approximately 72×36 pixels), which is visible at the anterior surface,can be matched by the imager on the posterior surface. Given anillumination source for a marker (such as a tattoo or light emitter) onthe conjunctiva, movement of the conjunctiva can be tracked to theprecision of the display device resolution. In some of theseembodiments, the curved imager of the implant detector utilizes much ofthe same technology, such as the TFT backplane, also used for thedisplay device. This sensing method has the advantage of being free fromthe MRI limitation and being inherently immune to other confoundinginfluences such as magnetic fields or electrical interference. In someembodiments, the marker is placed on the conjunctiva as marker 1140inserted into the tube 1130 described above with reference to FIG. 11Eand FIG. 11F, or inserted as the detectable device 1154 of the paddlemarker of FIG. 11G to 11J.

In some embodiments, the illumination source (such as a fluorescent dotor light emitting diode) used as a glowing implant marker is placed onthe conjunctiva and the marker position is tracked using a sparse arrayof photo detectors in the prosthetic cover. Again, in some of theseembodiments, the glowing implant marker is placed on the conjunctiva asmarker 1140 inserted into the tube 1130 described above with referenceto FIG. 11E and FIG. 11F, or inserted as the detectable device 1154 ofthe paddle marker of FIG. 11G to 11J. This sensing method is also freefrom the MRI limitation and immune to other confounding influences, andhas the further advantage of consuming less space and power. Suchembodiments use a much smaller array of photo detectors in a non-imagingconfiguration. The intensity at nearby photodiodes is used to computethe distance to the glowing implant marker. This approach istechnologically less demanding than development of a complete imager andrepresents a lot less information that needs to be digested by the localprocessor 301. The result is determined in many fewer computationalcycles, hence consuming less power by the processor. This sparse opticalsensor array uses approximately 24 individual photodiodes, each of whichhas very low power consumption, compared to 2592 photodiodes for a 72×36element imager.

In some embodiments, an array of illuminators, such as light emittingdiodes (LEDs), are used to excite a fluorescent implant marker,presumably once per display frame, e.g., at about 20 Hz. In some ofthese embodiments, there is a sparse array of such illuminators; and, insome embodiments this sparse array of illuminators is matched to thearray of optical sensors. Such illuminators are major power consumersfor many of these embodiments. Fortunately, the fluorescent implantmarker is useful even when it is not very bright, since it emits in adarkened environment when the illuminators are switched off, and thephotodiodes are extremely sensitive. So, in such embodiments, totalpower consumption of the illuminators and photodiodes are acceptablylow. In order to reduce power consumption, in some embodiments, theseilluminators are not used all at once, since only a few would beline-of-sight to the fluorescent implant marker. In these embodiments,after the florescent implant marker is located, only the one illuminatorthat is closest is turned on. This pumps up the fluorescence while usingthe least possible illuminator power. If executed at the display framerate, it suggests that the fluorescence half-life of the fluorescentimplant marker should be at least a few frame times.

There are many common fluorescent materials to choose from for variousembodiments. In some embodiments, quinine is used as a fluorescenttracer because quinine is a really bright emitter that's harmless ifingested in small quantities. Various fluorescent materials are used formedical procedures and are involved in some embodiments. For example, insome embodiments Fluorescein, which is used to visualize blood flowduring ophthalmic exams, is used as a glowing implant marker.

In various embodiments, the fluorescent material used as the glowingimplant marker is selected based on one or more of the followingconsiderations. In some embodiments other emitters are used, such achemical-luminescent or bioluminescent materials that emit light as aresult of an internal chemical interaction, or materials that absorblight quickly and emit over an extended time on the order of one frameduration at the same optical wavelengths. For example, in someembodiments, “Luciferase” is used. The chemical mechanism for lightemission from Luciferase is a reaction involving oxygen andAdenosine-5′-triphosphate (ATP).

For fluorescent and other light emitting materials, activatingwavelength (usually expressed in nanometers, nm, where 1 nm=10⁻⁹ meters)is well matched to an available LED illuminator. Emission wavelength isdesirably in a range from about 500 nm to about 1000 nm. The shorterwavelengths can be detected more efficiently (if matched to a suitablephotodiode) and they suffer less background noise from the patient's ownblack body radiation. The efficiency of converting activation wavelengthpower into fluorescent wavelength power (also called quantum efficiency)is desirable above 50%. This will dominate overall power consumption ofthe position detector. It is desirable for the fluorescence timeconstant (e.g., decay time) to be short, such as equal to just a fewframe times, as described above. Some embodiments use materials thathave very long time constants, e.g., many hours. In some of theseembodiments, this type of material is activated up in the morning (e.g.,using an external light source) and then would fluoresce for the entireday. This yields the lowest power consumption and smallest battery packfor the ocular prosthesis. Long term stability is desirable so that thefluorescent implant marker survives in-vivo for at least a year andpreferably much longer. A bio-compatible material is used in someembodiments so that the marker can be placed on the conjunctiva like atattoo mark. In other embodiments, the marker is encased in a durablebiocompatible container that is transparent, such as the tube 1130 asdescribed above with reference to FIG. 11E and FIG. 11F, or paddlemarker described with reference to FIG. 11G through FIG. 11J. ExistingFDA approval simplifies the adoption of a fluorescent emitter as theglowing implant marker.

In some embodiments a single light emitting diode (LED) is used as theglowing implant marker instead of or in addition to the fluorescentimplant marker. Suitable visible band LEDs are packaged in a surfacemount 0201 style. This package is a rectangular solid that is 0.010inches (0.25 mm) square by 0.020 inches (0.5 mm) long. The LED can fitinside a tube that is about 0.025 inches (0.64 mm) diameter. Flatteningthe ends of the tube (a bit like a kayak paddle), as depicted in FIG.11F, stabilizes the implant so that the LED shines in a predictabledirection. In some of these embodiments, the ends of the tube includenon-magnetic conductors that form an electric field antenna or inductioncoil that can be powered from a radio frequency transmitter in or usedby the implant detector of the ocular prosthesis, causing the LED toglow. An advantage of using an electric field antenna instead of aninduction coil, is that the antenna will not overheat when subjected tothe strong magnetic fields of a MRI device.

The encapsulated LED is similar to other structures already accepted bythe conjunctiva, so it should be well tolerated by the patient. Also,the materials used in the implant are safe for use in intense magneticfields, so the implant can stay in place during an MRI exam. The amountof light needed from the LED is quite small, perhaps a few microwatts.The LED is powered for approximately 1 millisecond out of each frame of59 milliseconds or longer, so the duty cycle is less than about 2%. Thismeans that the transmitting antenna can be activated with manymilliwatts of electrical energy to compensate for energy losses in thesystem, while consuming only a small percentage of the available batterypower.

The placement of photodiodes on the posterior surface of the orbitalimplant is affected by the line of sight between the photodiode and themarker, which is limited because the marker is on a curved surface. FIG.13A is a block diagram that illustrates an example radius of a field ofview of a photodiode disposed in the ocular prosthesis, according to anembodiment. The orbital implant 1300 (and conjunctiva) has a radius R11304 of about 12.5 mm from a center 1302 of the orbital implant in anocular prosthesis system for an adult. The photodiode is displaced fromthe surface of the orbital implant (and conjunctiva) by an air gap ofsome degree and the depth of the photodiode behind the posterior surfaceof the ocular prosthesis, which depth is desirably transparent to light.Thus the distance R2 1306 from the center 1302 of the orbital implant tothe position o1322 of the photodiode is greater than R1 by ΔR, whichvaries in various embodiments from about 0.5 mm to about 3 mm. Theimplant marker is on the horizon of the photodiode field of view at anangle φ that depends on R1 and R2 (or ΔR) as given by Equation 5.

φ=arccosine(R1/R2)=arccosine(R1/(R1+ΔR))  (5)

The dependence of φ on ΔR is listed in FIG. 13A, which shows that φvaries in various embodiments from about 16 degrees to about 36 degrees.Therefore, in some embodiments, the photodiodes are disposed just 2 mmabove the ball to achieve approximately a 60 degree field of view (30degrees to either side of the photodiode). Gaining a bit more heightwidens the view, but not very quickly. For instance, in someembodiments, a 72 degrees field of view is achieved for photodiodesdisposed at a height of 3 mm above the orbital implant (andconjunctiva).

Using the 2 mm height and maximum rotation of the orbital implant(called “ocular deflection” hereinafter) of +/−60 degrees horizontallyand +/−45 degrees vertically as an example, it only takes a few sensorsto keep the implant marker in view at all times. However, it takes quitea few sensors before there is enough coverage so that the implant markeris always within view of multiple sensors at the largest oculardeflection angle. FIG. 13B is a block diagram that illustrates exampledistribution of photodiodes disposed in the ocular prosthesis to detectmovement of an implant marker that moves with the orbital implant andemits light, according to an embodiment. The orbital implant 1300 isdepicted in horizontal cross section with conjunctiva 14 into which hasbeen attached the glowing implant marker 1310 (either fluorescent dot orLED, or some combination, in various embodiments). In some embodiments,the glowing implant marker is the detectable device 1154 in the paddlemarker 1150. Also depicted is ocular prosthesis 1330 that includesmultiple positions 1322 for photodiodes. Horizontal ocular deflectionsof 0 degrees at ray 1304, 30 degrees at ray 1305 a and 60 degrees at ray1305 b are also depicted. When the horizontal ocular deflection is 60degrees, the implant marker is on the 60 degree ray 1505 and is visibleto a photodiode at a position on the 30 degree ray 1305 a, but not to aphotodiode at a position on the 0 degree ray 1304. Therefore additionalphotodiodes are includes at additional positions, such as on the 60degree ray 1305 b. To insure coverage by three photodiodes, additionalpositions are added.

In one set of embodiments, about 12 photodiode positions are distributedon the 60 degree deflection circle as shown in FIG. 13C and FIG. 13 D.FIG. 13C and FIG. 13D are block diagrams that illustrates exampleoverlapping fields of view of multiple photodiodes disposed in theocular prosthesis, according to various embodiments. FIG. 13C is adiagram that illustrates example positions for photodiodes on or withina posterior surface of an ocular prosthesis, according to someembodiments. FIG. 13C depicts the center 1334 of the posterior surfacethat corresponds to the 0 degree deflection ray 1304 of FIG. 13B, a 30degree circle 1335 a on the posterior surface that intersects the 30degree ray 1305 a of FIG. 13B, and a 60 degree circle 1335 b on theposterior surface that intersects the 60 degree ray 1305 b of FIG. 13B.A photodiode position is at the center of photodiode field of viewcircle 1330. To obtain at least two sensor coverage of each 60 degreeocular deflection, 12 photodiode fields of view 1330 overlap bypositioning each photodiode 30 digress along the 60 degree circle 1335b. Even with a photodiode position at the center 1334, there are manypositions where the implant marker is in view of only one photodiode,e.g. at areas 1336.

Placing a second ring of sensors on the 30 degree deflection circle 1335a provides the desired coverage, plus highly overlapped coverage in thecentral field of the eye. This arrangement is shown in FIG. 13D. FIG.13D is a diagram that illustrates example positions for photodiodes onor within a posterior surface of an ocular prosthesis, according to someembodiments. FIG. 13D depicts the center 1334 of the posterior surface,the 30 degree circle 1335 a, and the 60 degree circle 1335 b. Aphotodiode position is at the center of photodiode field of view circles1330. In this embodiment, 12 photodiode positions are added, arrangedevery 30 degrees along the 30 degree circle 1335 a. Thus completecoverage with multiple photodiodes is achieved with 25 photodiodes. Insome embodiments, the photodiode at the center is consideredsuperfluous, and it is omitted, leaving the total number of photodiodesat 24. In other embodiments, other photodiode positions are alsoeliminated, or shifted, or both to reduce the complexity and computationload and power consumption of the optical implant detector. In someembodiments, one or more other photodiode positions are added.

In another embodiment, adequate coverage can be obtained by placing asingle LED in the conjunctiva 14 at the zero degree ray 1304 of theorbital implant, as depicted in FIG. 13B, then a ring of about 6 opticalsensors (e.g., photodiodes) at the 60 degree circle 1335 b depicted inFIG. 13C and FIG. 13D and a second ring of 12 sensors at the 30 degreescircle 1335 a depicted in those same figures, for a total of 18 opticalsensors (e.g., photodiodes). With this geometry in mind, physical sizebecomes an important characteristic for the photodiodes.

Most optical sensors are packaged in pretty large hermetically sealedhousings, typically 5 to 6 mm in diameter. Unpackaged chips are notreadily available since a p-type/intrinsic/n-type semiconductor (PINdiode) used in many photodiodes has stringent packaging requirements.Ultimately nearly identical PIN diodes were identified from Hamamatsu(110805S10625) and Advance Photonics (PDB-C154SM).

For the wearable version, a similar sensor in a small surface mountpackage, or else as an unbonded die that can be attached directly to aflexible circuit card. These devices are inexpensive, around $1.00 inmodest volume, suitable for an affordable prosthesis. For example, theHAMAMATSU™ 110805S10625 package is only 2.7 mm by 3.2 mm with an activearea of 1.3 mm by 1.3 mm, and is suitable for use as a photodiode at the12 positions along the 30 degree circle 1335 a and is suitable for usein the ocular prosthesis depicted in FIG. 20, described in more detailbelow. Peak spectral response is at 940 nm (near infrared) falling toabout 50% in the visible region (480 nm). Spectral sensitivity isapproximately 550 mA per watt of illumination. Typical dark current is 2pA at 1V reverse voltage, dropping to 0.1 pA at 10 mV bias. But themaximum dark current is much larger, at 10 nA. Maximum detector currentis about 2 μA with 100% illumination. Noise equivalent power is 0.15 pWper square root Hz (bandwidth). Wide field of view is 133 degrees FullWidth at Half Maximum, with better than 90% response over the desirable+−30 degree field of view.

A typical optical sensor is the HAMAMATSU™ 82386 line of siliconphotodiodes from HAMAMATSU PHOTONICS K.K.™ of Hamamatsu City, Japan.These devices work well in the near infrared, with best sensitivity inthe 800 nanometer (nm, 1 nm=10⁻⁹ meters) to 1000 nm range of opticalwavelengths. The S2386-18K is packaged as a TO-18 which is a 5.4 mmdiameter can, a potential choice for an experimental bench model of theocular prosthesis, described in more detail below. Using the S2386-18Kas an example, the field of view is well matched to the embodimentsdescribed above, yielding more than 80% response throughout a 60 degreeaperture (+/−30 degrees). Peak spectral sensitivity is 0.6 amperes perwatt. Response times (depending on the load resistance) are in the 1 μsrange. So this sensor is capable of being quickly powered up to take alook at the field of view and then de-activated to save power. Inoperation, the photodiode gets back biased by a few volts and exhibitsroom temperature leakage (dark current) of less than 10 pA. So powerconsumption is imperceptibly small even if the sensor is energized allthe time.

Using this sensor as an example, the desirable properties of the glowingimplant marker can be determined for various embodiments. The glowingimplant marker desirably emits more optical power than the sensor darkcurrent, even when viewed at the maximum distance and angle. A baselinecomputation of the required optical power is performed by assuming thatthe glowing implant marker emits its power uniformly over ahemispherical area. The maximum viewing distance is approximately R1*tan(30 degrees), which equals 7.2 mm for R1=12.5 mm. The hemisphere of thisradius has surface area 2πR1 ²=327 mm². The example sensor has an areaof 1.2 mm² so the sensor intercepts approximately 0.4% of the lightemitted by the glowing implant marker. Using a sensor efficiency of 80%(at maximum viewing angle)×0.6 amperes/watt (sensitivity), it isdetermined that the glowing implant marker preferably emits 5.6 nW ormore to raise a sensor current that is at least double the 10 pA darkcurrent.

The detectors operate at very low power but it is desirable to operatethe detectors at the lowest possible light level, especially forembodiments that use illuminators to power a fluorescent implant marker.Detector circuits often apply a reverse bias to the photodiode. Thereverse bias minimizes the capacitance of the detector and therebyimproves frequency response. But the penalty is increased dark current.Applicant's approach is to operate the PIN diode at zero bias voltage.In theory, this reduces the dark current to zero. Light input createscharged pairs in the detector, resulting in a current that can bemeasured.

In many embodiments, the photodiode output is amplified for furtherprocessing. To avoid amplifying ubiquitous 60 Hertz electromagneticsignals in the environment, careful design of the amplifier was found tobe desirable for some embodiments. The noise equivalent power for thediode suggests a noise floor of less than 10 pA for the detector, so anamplifier that could work at such small currents is desirable for someembodiments. The amplifier circuit is described in more detail below.

To evaluate the performance of various optical implant detectorembodiments, a bench model was constructed as an experimental ocularprosthesis system to test measurements, circuitry and processingembodiments. This allows not only testing of position sensing methods,selection of appropriate optical sensors, and evaluation ofsignal-to-noise, but also allows the determination of achievablepositioning accuracy. FIG. 14A through FIG. 14C are block diagrams thatillustrate example test equipment used to demonstrate determiningexperimental orbital implant movement based on an light emitting implantmarker and photodiodes arranged as on an ocular prosthesis, according toan embodiment. FIG. 14A though FIG. 14C are images rendered by a threedimensional computer aided design (CAD) software package calledSolidWorks from Dassault Systemes SolidWorks Corporation of Waltham,Mass. operating on a general purpose computer, such a described belowwith reference to FIG. 21.

FIG. 14A is a block diagram that illustrates an example perspective viewof the bench model 1400. Onto a bench 1402 with hole 1405 are mounted afirst servo motor 1410 a and a second servo motor 1410 b that rotate afirst Scotch yoke 1412 a and a second Scotch yoke 1412 b, respectively,around perpendicular axis representing horizontal and vertical rotationsof an eyeball. Each driver translates from a pulse width modulated (PWM)electrical signal to a rotary position. A ball 1416 is placed above thehole and is constrained from moving upward away from the bench by acollar 1418. A post 1414 is attached to the ball and passes though slotsin both yokes 1412 a and 1412 b. As the yokes 1412 a and 1412 b rotatewhen driven by the servo motors 1410 a and 1410 b, respectively, thepost 1414 is pushed by the yokes to change orientation. The post 1414 isattached to the ball, so that when the orientation of the post 1414changes, the ball 1416 rotates in response to operation of the servomotor 1410 a or servo motor 1410 b or both. FIG. 14B is a block diagramthat illustrates an example different perspective view of the benchmodel 1400, showing the same elements described above. The rotation ofthe ball 1416 represents the rotation of the orbital implant 120 and isconsidered a experimental for the orbital implant in the followingexperimental embodiments.

FIG. 14C is a block diagram that illustrates an example vertical crosssectional view of the bench model 1400. The yoke 1412 a, yoke 1412 b,post 1414, ball 1416 and collar 1418 are as described above. A bowl 1420is disposed in the hole 1405 and mounted to the bench 1402 from below.The upper curved surface of the bowl 1420 represents the posteriorsurface of the ocular prosthesis, and the bowl 1420 is considered aexperimental ocular prosthesis in the following experiments. A lowercollar 1422 disposed above the bowl is supported in place by the bowl1420. The lower collar 1422 supports the ball 1416 and prevents the ball1416 from falling through the hole or touching the upper surface of thebowl 1420. The ball 1416 is thus free to rotate between the lower collar1422 and the collar 1418 as the ball is rotated by the post 1414 that isimpelled by movement of the yokes 1412 a and 1412 b.

The implant detector system according to various embodiments is testedexperimentally by disposing on the ball 1416 a LED 1430 as a glowingimplant marker, and disposing along the upper surface of the bowl 1420multiple photodiodes 1440. When the post is vertical, the experimentalorbital implant is considered to be at rest as if a subject were staringstraight ahead.

The Bench Model 1400 is built using a combination of Stereo Lithography(SLA) and Solid Printing. Both of these techniques are rapid prototypingmethods that directly use the SolidWorks data files to produce therequired mechanical pieces. The SLA method works in a liquid monomervat. A laser polymerizes the top surface, creating a cross section ofthe desired object that is about 0.04″ (0.1 mm) thick. This solidifiedlayer is lowered just below the surface of the vat and the next layer iswritten by the laser. Repeating this process builds up the entire objectin 0.1 mm steps. The Solid Printer works by jetting liquid polymer inlayers onto a solid stage. This produces a smaller layer thickness, asthin as 0.0005 inches (0.012 mm), which yields a better surface finishand improved detail. The two printing methods permit different materialchoices including a variety of hard and soft plastics that can be eitheropaque or optically transparent.

The ball 1416 is a stock item that can be purchased in differentmaterials ranging from Teflon to polycarbonate or ceramic. A hole getsdrilled for the post 1414 which is also a stock item available in carbonfiber for a good combination of low weight and high strength Fastenersare stock plastic or steel items. Each yoke rides on two pivots: thedriven end relies on the bearing inside the servo actuator; the free endis a steel pin (simple bushing).

To emulate a fluorescent dot, in some embodiments, the LED 1430 has a“frosted” plastic plug carrying a diffused light spot to the bottomsurface of the ball 1416. This permits varying the optical power andperiodicity as needed for the experiments. It was computed that only afew nanowatts of emitted power are sufficient for experimentalembodiments, so the drive current applied to the LED is quite small. Asmall array of photodiodes 1440 is fitted to a upper surface of the bowland then wired to an external circuit card that provides the electricalenvironment to energize the photodiodes and amplify their outputs. Ahigh speed wide dynamic range data acquisition system borrowed from anFTIR infrared spectrometer was used to digitize the signals to valuesthat were output to a spreadsheet form for analysis. In someexperimental embodiments, the space between the bowl 1420 and ball 1416is filled with saline solution to mimic the natural environment of theprosthesis.

The central photodiode was placed at the center of the upper surface ofthe bowl 1420, and the servo motors were used to drive the ball tovarious positions while measuring the detector response. The motordrives are quite accurate, so they provide a reproducible way ofselecting exact positions.

For some bench test embodiments, a long lifetime green fluorescentmaterial was used which was activated with a hand held ultraviolet (UV)lamp. The light output from this material decayed over a number ofminutes, allowing the diminishing detector signals and the response atvery low signal levels to be observed. A digital voltmeter (DVM) of aFLUKE™ multi-meter from FLUKE CORPORATION™ of Everett, Wash. was used tomeasure the output of the detector circuit, manually recording thereadings into an Excel spreadsheet.

FIG. 15A is a table that illustrates example variation of detected lightintensity with angular separation between photodiode and light emittingimplant marker, according to an embodiment. The two left columns 1512 aand 1512 b indicate a pair of X-positions for the motor driven ballusing the first servo motor 1412 a. “6000” represents the centerposition for the ball (the Y-axis using the second servo motor 1412 bwas always centered during this run). An excursion of 1000 countsrepresents 30 degrees of rotation. Each row 1514 a through 1514 vcorresponds to a different step in the sequence of measurements. Foreach step of the sequence one reading was taken at center and anotherreading at some deflection angle. The digital voltmeter (DVM) readingsare in microvolts and reported in columns 1512 c and 1512 dcorresponding to X-positions in columns 1512 a and 1512 b, respectively.As can be seen from the “DVM at 6000” column, the light output of thefluorescent dot dropped significantly during the course of the data run.By the time the deflection of 7050 counts (about 32 degrees) wasmeasured, the signal response had dropped off quite a bit. This is theexpected result as it corresponds to nearing the local horizon as seenfrom the multi meter vantage point 3 mm from the surface of the ball.

In this experimental embodiment depicted in FIG. 15A, an inputmultiplexer is used to selects one of several photodiode inputs to bedelivered to an analog to digital (A/D) converter for sampling. Themaximum voltage is 720 μV which corresponds to 90 pA. The smallestvoltage is 263 μV or about 33 pA input current. Almost all of thislatter current is leakage from the multiplexer, not current from thephotodiode. This bench circuit is stable to about 10 or 15 μV whichequates to 1 or 2 pA. In this context, the 30+ pA multiplexer current isseen to be a significant offset to the desired measurement. When thisbackground (dark) current is subtracted from each reading, then thedifference between the center (6000) and deflected (point) valuesindicate how much detector response is achieved.

FIG. 15B through FIG. 15E are graphs that illustrate example variationsof detected light intensity with angular separation between photodiodeand light emitting marker on a experimental orbital implant, accordingto various embodiments. FIG. 15B is a graph 1520 for the deflectionresponse with the multiplexer (mux) and including the subtraction step.The horizontal axis 1522 is X-position in servo motor step size. Thevertical axis 1524 is percent brightness compared to the start of theexperiment at a position directly in front of the glowing implant marker(e.g., the fluorescent dot). Trace 1526 indicates the response todeflection with the input multiplexer and the dark current subtractedout.

The data points of trace 1526 are 50 counts apart. This step sizeequates to just over one pixel at the display device. A rather linearresponse is indicated out to about position 7000 which represents 30degrees deflection. The bump at 6800 was seen regularly which suggestsit's an artifact such as a reflection. The response curve flattens atcenter and again as 30 degrees deflection is approached. Both behaviorsare well predicted by the geometry of the ball and detector. But thenearly linear response is a surprise. The geometry suggests that thedetector response should falloff much more sharply (in the order ofdistance squared) with increasing deflection. The linear response can beexplained if reflections are occurring off the bowl or ball, or both.The energy from the reflections, while attenuated, combines with theenergy from the direct path to produce a response that is proportionalto distance, very much like the action of a waveguide. This linearresponse means that the detection system can work with less dynamicrange than expected, thereby improving measurement quality, provided theconjunctiva over the orbital implant or the posterior surface of theocular prosthesis, or both, are reflective at the wavelength of theglowing implant marker.

FIG. 15C is a graph 1530 for the deflection response without themultiplexer (mux). The horizontal axis 1522 and vertical axis 1524 areas described above. Trace 1536 indicates the response to deflectionbypassing the input multiplexer to eliminate its dark current. Themaximum measured current was about 45 pA in this experiment and theminimum was quite close to 0 pA. Removing the pedestal current from themux improves the data slightly, but the qualitative result remains thesame. It is easy to estimate the deflection to an accuracy of about onepixel.

FIG. 15D is a graph 1540 for the deflection response without themultiplexer (mux) and with 25% of the light used in FIG. 15C. Thehorizontal axis 1522 and vertical axis 1524 are as described above.Trace 1546 indicates the response to deflection with a weakerfluorescent source. Maximum detector current was about 15 pA in thisexperiment, hardly above the 10 pA noise equivalent power for thedetector. The data are obviously not as good at this light level, butstill quite usable.

FIG. 15E is a graph 1550 for the deflection response without themultiplexer (mux) using a different photodiode. The horizontal axis 1522and vertical axis 1524 are as described above. Trace 1556 indicates theresponse to deflection with the ADVANCED PHOTONIX™ photodiode. Maximumdetector current was about 38 pA for this experiment. The data are notqualitatively different from the Hamamatsu photodiode. This is anencouraging result since it indicates two different sources for thephotodiodes of the optical implant detector.

Based on the results from the above experimental embodiments, thecircuit components were determined for processing the output fromvarious photodiodes in various embodiments.

FIG. 16A is a photograph that illustrates an example test equipmentcircuit board 1600 configured to measure relative intensity at multiplephotodiodes to determine orientation of the experimental orbitalimplant, according to an embodiment. The circuit board has two cutouts1602 a and 1602 b so that it can mount to the mechanical model 1400 ineither of two positions. The ring of objects around each cutout is thegroup of tiny coaxial connectors 1604 that bring in the photodiodesignals from the bowl. This approach avoids a cost problems encounteredwith constructing prototype flex connectors to do the same job. The dualmounting locations allow exploration of two different circuitembodiments for the optical implant detector. Each circuit utilizes thesame array of 16-photo-stmsors and the same single-chip computer tosample the results. The two circuits differ in the way the sensors getconnected to the microprocessor. One circuit is optimized for highestperformance, e.g., low leakage and best signal to noise. The other oneis optimized for small size and low cost.

FIG. 16B is a block diagram that illustrates an example circuit on acircuit board of FIG. 16A configured to measure relative intensity atmultiple photodiodes, according to an embodiment. In general, thecircuit components include, for each photodiode 1620, a pair of matchedpreamplifiers 1630, a differential amplifier 1640 and a multiplexer1650. Data from the multiplexer 1650 are processed by processor 1660 todetermine deflection of the experimental (experimental) orbital implant.In various embodiments, processor 1660 is the same as the ocularprosthesis processor 301 or a separate processor in the implant detector309, or some combination.

Dual matched preamps are built around a Linear Tech LTC6241CS8 devicefrom LINEAR TECHNOLOGY CORPORATION™ of Milpitas, Calif. Each inputamplifier is a current-to-voltage converter that uses a 4 megaohm (MΩ, 1MΩ=10⁶ ohms) feedback resistor (actually constructed from four 1 MΩresistors in a packaged array). This is the largest off-the shelffeedback resistor located. Ultimately this resistor sets bothsensitivity and bandwidth. With the circuit as shown, sensitivity of 8volts per μA of input current is achieved and a bandwidth of about 15kHz. This is more bandwidth than is desirable to use; and, as the benchresults show, additional sensitivity is desirable. In some embodiments,an even higher value feedback resistor is used to obtain moresensitivity at somewhat lower bandwidth. Note that the matched inputpreamps conspire to keep the photodiodes at zero bias voltage. Both endsof the photodiode get driven to a particular voltage designated Vcm butthe differential voltage is quite small, essentially just the offsetvoltage of the preamps and multiplexer. This setup drives the photodiodedark current to essentially zero for best sensitivity.

Outputs of the matched preamps get summed in a unity gain differentialamplifier. This removes common mode voltages to eliminate 60 Hz noiseand other environmental electromagnetic contamination. The differentialoutput of this amplifier can drive an analog to digital (A/D) converteror, in some embodiments, the experimental instruments. In the benchtests, it was found that the noise floor achieved by this configurationwas quite low, permitting meaningful outputs in the low microvolt range.In other embodiments, more voltage gain is applied to this signal beforedriving an A/D converter.

A full array of detectors uses a multiplexer, such as multiplexer 1650,to connect various photodiodes to a measurement circuit. The ANALOGDEVICES™ ADG734BRUZ from ANALOG DEVICES INC.™ of Norwood, Mass., is asuitable integrated multiplexer. In some embodiments, it is used in aT-switch configuration that keeps the detectors at the same bias pointwhether selected or not. This improves settling time as it switches fromone detector to the next. The leakage current specification for themultiplexer is greater than a desirable 10 pA goal, so this affects thedesign of various embodiments.

The high performance/high cost/large size option uses full differentialT-Switch connections. The multiplexer connects both terminals of theselected photodiode to a fully differential amplifier, as shown in FIG.16B. This allows suppression of noise from external electrical sources.Each unconnected sensor has both terminals grounded. This preventsunwanted charge (photo-electrons) from accumulating during the “off’time of the sensor so there is no discharge or arcing when reconnectingto it.

The minimum acceptable performance option uses singled ended switch andamplifier. The multiplexer just connects the “hot” terminal of theselected photodiode to a single ended amplifier. All of the sensorground terminals are connected to a common bias point. This is a simplerscheme with less noise rejection.

Testing revealed that the single ended switching matrix was too noisy toprovide reliable data, so the results reported here are for the fullT-switch implementation. Further tests indicate that the moreadvantageous feature of the complex multiplexer is its differentialnature. The T-Switch feature (grounding each sensor when not selected)consumes half the resources of the multiplexer but adds little to signalquality.

Sensors are attached to the bench model circuit card using miniaturecoaxial cables and connectors. This is adequate for bench testing. Inproduction embodiments, it is desirable to use flex circuitry to housethe photodiodes and route their signals back to the A/D converter. Insome embodiments, the multiplexer circuitry is distributed onto the flexcircuit to minimize trace length and improve noise performance. Thiswould likely make the production version of the sensor even more noiseimmune than the bench test embodiment of the circuit. The bench modelsensor circuits have an input stage consisting of a current to voltage(I-V) converter (400 kiloohm, kΩ, feedback resistor, 1 kΩ=10³ ohms) anda voltage gain stage (16 fold gain) for an overall gain of 6.4 volts/μA.The KINETIS central processing unit (CPU) processor, from FREESCALESEMICONDUCTOR INC.™ of Austin, Tex., has an A/D converter with 1.2 Voltsinput range and (effectively) 12 bit resolution. This makes one leastsignificant bit (LSB) at the A/D converter equal to 46 pA at bandwidththat is approximately 15 kHz. Settling time is limited by thephotodiodes which are operated at zero bias voltage in order to minimizedark current. The photodiodes develop their maximum capacitance(typically 100 pF) at zero bias, so the resistor-capacitor (RC) circuittime constant developed via the preamp feedback resistor is 100 pF×400kΩ=40 μs. This is validated by the desirable settling time of 160 μs(four RC time constants=98% settling) before taking each sensormeasurement.

Static measurement were obtained by moving one axis of the servo whilecollecting optical sensor output from a microprocessor. FIG. 17A andFIG. 17B are graphs that illustrate example variations of detected lightintensity with positive and negative angular separations betweenphotodiode and light emitting marker on an experimental orbital implantusing the circuit of FIG. 16B, according to various embodiments. FIG.17A is a graph 1700 that illustrates example results from an embodimentof an experimental setup. The horizontal axis 1702 is deflection anglein degrees. The vertical axis 1704 is photodiode circuit response incounts (arbitrary units). Trace 1706 depicts the measured response ofthe high performance circuit to deflection of the experimental orbitalimplant. Note that the peak intensity is not at the center of the plot.This just indicates that the zero point of the servo motor system isn'tdirectly in the center of the sensor array. Trace 1706 shows that sensorresponse is non-linear, falling off rapidly with distance, which is theexpected result. If our light source (an LED) were a homogenousradiator, the intensity would fall off as distance squared because thedetector is of constant size and the surface area of a sphere isproportional to radius squared. In the experimental embodiment, the LEDis mounted on a sphere which is rolling away from the sensor. As thelight source nears the local horizon, intensity falls rapidly to zero.This leads to another nonlinear term which probably behaves as distanceto the power of x, where x is different from 2 and determined byexperiment. Hence the overall distance vs. intensity relationship is ahigh order exponential function.

FIG. 17B is a graph 1710 that illustrates example results from anembodiment of an experimental setup with intensity raised to the 0.1power. The horizontal axis 1712 is deflection angle in degrees. Thevertical axis 1714 is photodiode circuit response intensity raised tothe 0.1 power. Trace 1716 depicts the measured response of the highperformance circuit to deflection of the experimental orbital implant.This data transform makes the plot look almost linear. The real lessonfrom this graph is that, even though the intensity values near +−30degrees are small, they are still changing in a way that allows usefuldeflection data to be derived from the optical experiment. This makes itclear that these sensors can be used for triangulation of the lightsource.

Signal to noise ratio (SNR) for these measurements is good. In someembodiments, the KINETIS™ A/D converter is configured to take more thanone input sample (5 μs each) per digital output. When 16 samples aretaken per reading (80 μs) the signal has a standard deviation of 1.3counts and a peak deviation of about 5 counts. This amounts to 10 or 11bits of useful information from the A/D converter at a typicalillumination level (about 100 nA maximum at the photodiode). Goodtriangulation can also be obtained with lower SNR than this ifillumination intensity is reduced or the observation period isshortened. It takes about 160 μs for the signal to settle after a changein the multiplexer setting, so the present 80 μs observation periodresults in 240 μs per multiplexer setting or about 4 μs to scan theentire array of 16 photodiodes.

From the standpoint of power consumption, it is advantageous to shortenthe total observation time so that the circuitry can spend more time insleep mode. This is accomplished, in some embodiments, by first making afast scan of the photodiodes (50 μs each) and then returning to thebrightest three or four for a closer look (240 μs each). In this way,the total time is reduced to less the 2 ms or about 4% of theapproximately 50 ms frame time (20 Hz display refresh rate).

It was found that the optical sensor works nearly equally well withsaline or air in the gap between the LED and the sensor bowl. Actually,sensor intensity is a bit better with the saline in place. The datacollection algorithm makes an estimate of the dark current (background)from each sensor. In some embodiments, the background gets subtractedfrom the foreground value to obtain an intensity figure.

The sensor array is strongly affected by ambient light, for instancefluorescent lighting with its 120 Hz oscillations. So it is advantageousto provide some shielding from a bright environment. This should beprovided by the prosthesis itself, in some embodiments. Small amounts oflight leakage are tolerated well. It was determined that whenever theLED is activated, the entire ball 1416 glows somewhat. This backgroundglow amounts to about 15 counts at the A/D converter compared to peakintensities of 3000 counts. The glow gets treated as background signalso it does not affect the deflection computation.

The basic components of the circuit of FIG. 16B, such as microprocessor,sensors, multiplexers, and amplifiers are suitable for operation atextremely low power levels of the ocular prosthesis. Thus, it is usefulto take a look at steady state power consumption to see what it impliesabout battery life. FIG. 16C is a table that illustrates example powerconsumption of various components of the optical sensor circuitry,according to some embodiments. The table of FIG. 16C shows that theexample circuit typically consumes about 90 mA in its active mode. Thiswas confirmed by direct measurement of 85 mA active current. Powerconsumption falls into the low micro-amp range when the circuit is insleep mode (not sampling the sensors). With powered up active time at4%, in some embodiments, this circuit consumes about 3.6 mA on average.Power consumption is further reduced, in some embodiments, by using asmaller number of sensor amplifiers. The illustrated design minimizesthe number of multiplexers (to improve SNR) at the cost of extraamplifiers, but this precaution did not provide a great advantage. Sincethe multiplexer chips consume almost no power, the larger multiplexer ispreferred. This reduces power consumption by about 30%.

The largest power consumer is the KINETIS™ K10 processor which isoperating at 100 MHz. This chip has a lot of on-board resourcesincluding 512 kilobytes (kB, 1 kB=10³ bytes, 1 byte=8 bits) of Flashmemory, so it consumes quite a bit of power. For sensor handling alone,the power consumption is cut quite a bit. A typical figure for a smallprocessor configuration is 160 μW per MHz which would lead to an activecurrent consumption of just 5 mA and an average current consumption ofabout 200 μA. A major contributor to processor power consumption is thecomputation used to form the image for the display device. The amount ofmemory and the number of computational cycles used to update the displayevery frame (about 50 ms to 60 ms) will dictate how much CPU capabilityis included in various production embodiments. Efficient algorithms fordisplay device updates conserve power in order to optimize battery life.

The present figure of 3.6 mA average for the entire circuit is near themaximum for our planned batteries. Current to the LED beacon wasmeasured at 1.65 mA peak, which, using a 4% duty cycle, consumes onaverage about 66 pA. This is well within the power budget forillumination. In some embodiments, this power is delivered via radiofrequency transmission, which is somewhat lossy. However a ten-foldpower loss does not pose a threat to battery life.

FIG. 18A is a block diagram that illustrates an example arrangement ofphotodiodes to detect motion of an experimental orbital implant with alight emitting marker, according to an embodiment. A photodiode isdisposed at the center, five photodiodes are disposed equally around atabout the 30 degree circle, and ten photodiodes are disposed equallyaround at about the 60 degree circle. Both qualitative and quantitativemeasurements for dynamic performance of the optical implant detectorwere favorable.

The qualitative evaluation used the servos to “play back” an actual eyemotion file supplied by MSKCC personnel. Real time position data fromthe sensor array were collected during playback. Using a personalcomputer, a human face was displayed with two computer driven eyes. Oneeye was driven by the original eye motion file that drove the servomotors of the bench model, and the other eye was driven by the sensordata from the bench model eye. When the eye is moving slowly or is atrest, the position sensor solution oscillates between two adjacentpixels. This is expected for any practical sensor, but it produces ajittery looking eye display. An anti-jitter algorithm was implemented tosuppress small changes that were non-repeating; and, this step removedthe display artifact. Even though the servo motors were fairly powerful,rapid eye motions (cycads) produced such high velocities that the servomotors were unable to keep up. This produced a small amount of lag whichwas visible on the two eye display. However this is not a problem for aproduction embodiment in which the orbital implant is driven by thesubject and not by servo motors.

A quantitative test included stepping the servos through every possibleposition of the mechanical eye, taking multiple sensor measurements ateach position. This data was imported into Excel spreadsheets and usedto generate plots. While the servo was making 1 degree steps in theX-axis, 9 separate readings of the 16 sensors were taken at eachposition.

As expected, these data show some scatter. The sensitivity of the PINdiode photodiode array changes with position. When the LED beacon islocated directly beneath one of the 16 PIN diode photodiodes, there isexcellent signal amplitude and position sensitivity. When the LED isequidistant from the three nearest sensors (in the middle of atriangle), signal amplitude and position sensitivity are both reduced.The Euclidian distance between the sensor readings for adjacent servopositions are measured. This gives a sensitivity measure. Comparing thesensor uncertainty to this sensitivity gives a metric for accuracy.

FIG. 18B is a graph that illustrates example orientation confidence forthe experimental orbital implant using the photodiode arrangement ofFIG. 18A, according to an embodiment. The x axis 1812 indicatesdeflection in the X-direction in degrees (e.g., from rotation of thefirst servo motor 1412 a). The y axis 1814 indicates deflection in theY-direction in degrees (e.g., from rotation of the second servo motor1412 b). The z axis 1816 indicates the resolution confidence (in numberof position elements, called pels hereinafter) at the combineddeflection. Most of the surface enjoys good confidence (less than 0.5pels) indicated by the dark regions at low elevation. This level ofaccuracy provides very secure position data. There are spots of moderateconfidence (0.5 to 1 pels) indicated by the lighter regions. A fewcombinations lead to noticeable errors (1 to 1.5 pels). A few peaksindicate the largest errors of 1.5 to 2 pels.

FIG. 19A and FIG. 19B are graphs that illustrates example distributionsof errors with distance between light emitting marker and photodetectorsused to triangulate position of the marker, according to an embodiment.FIG. 19A is a graph 1900 that illustrates example data points sorted bynearest neighbor distance (NND). NND is a Euclidian measure across the16 sensors, summing the square of each sensor distance (in pels), thentaking the square root of the sum. The horizontal axis 1902 representsdifferent positions (orientations) for the experimental orbital implant.The right side vertical axis 1904 b indicates the nearest neighbordistance in pels. The left axis 1904 a indicates the position error inpels. Trace 1906 is the NND, according to which the data are sorted;and, therefore, trace 906 decreases continually from left to right.Trace 1908 indicates the error, which varies between adjacent sortedpositions by about 0.1 pels. When the sensitivity is at its best (rightnear or under a PIN diode) the NND distance is large (over one hundredpels, the measurement error is less than one quarter pel. The minimumNND is nearly constant throughout the motion field, averaging about 15pels. As trace 1906 declines to about this level, the error trace 908increases to about one pel.

FIG. 19B is similar to FIG. 19A but with 10% of the positions with thelowest sensitivity removed. This amounts to moving the sensors 10%closer together. This result shows that by placing the sensors a bitcloser together (might require 19 instead of 16 PIN diodes) all of thepossible eye positions have accuracy better than 1 pel.

It is noted that the bench model test embodiment used +/−60 degreestotal range in both the horizontal and vertical axes for simplicity inconstruction. The production embodiment of this sensor array implementsa reduced vertical deflection (e.g., about 45 degrees verticaldeflection) to mimic the human eye. The same number of sensors thenallows closer sensor spacing. This would further improve SNR since theoptical signals improve rapidly with shorter distance, as indicated inFIG. 19B. In some embodiments, 21 sensors disposed in three rings of 3,6 and 12 are used instead of the 16 sensors disposed at the center andin two rings of 5 and 10, described above.

In some embodiments, the implant detector 309 includes a practicalcircuit to drive the proposed LED implant marker. In some embodiments,this circuit uses a radio frequency (RF) transmitter. In theseembodiments, the implant marker includes the LED, and an LED powersource that includes, at least, a receive antenna. The RF driven LED isoptimized for low power consumption, small size, and a short transmitdistance. It is advantageous in various embodiments that the RF transmitantenna is also used for other purposes, such as in the communicationsmodule 313, or as the inductive coil for an inductive charger in chargereceiving device 305 to replenish the on-board battery 303, or somecombination. In some embodiments, the receiver in the implant marker isa dipole antenna which would respond to electric fields but not tomagnetic fields (to avoid being over-driven by the magnetic fields in anMRI machine).

2.4 Ambient Light Sensor

Some embodiments include an ambient light sensor 307. In someembodiments this functional block includes a phototransistor andassociated circuitry to filter, amplify and bias the output of thecircuit to produce an analog voltage proportional to the ambient lightlevel averaged over the normal human visual range. In some embodiments,the optics include appropriate optical filters to approximate the humanvisual response. The circuit output is interpreted by an A/D converter,which, in some embodiments is a peripheral sub-block of the CPU thatserves as processor 301. The technology, circuitry and components arewell known. The packaging and assembly aspects of this functional blockare described in a later section with the packaging of the othercomponents. One unique challenge relevant to this functional block ishow light will reach the phototransistor. In various embodiments, thephototransistor is mounted at the prosthesis anterior surface, or alight pipe or optic fiber channels light from the anterior surface tothe sensor. Because the display device covers much of the visiblesurface, a least visually intrusive configuration is chosen, such as asensor under the eyelid outside the display device, or a fiber port thatappears red, such as part of a blood vessel naturally seen on a scleraportion of an image or fixed background. In some embodiments, thesurface location is in the area of the tear duct. The light sensor isexpected to not significantly impact the power budget or battery life.

2.5 Processor

Various embodiments include a processor 301, of minimal or powerfulcapacity. In some embodiments, ultra-low power microcontrollers fromdifferent manufacturers are used, such as processors that have currentconsumption of 120 μA to 1000 μA per million instructions per second(MIPS). The MSP430 family from TEXAS INSTRUMENTS™ of Dallas, Tex., has anominal current draw of 165 μA to 400 μA per MIPS depending on theconfiguration and peripherals. The microcontrollers fromSTMICROELECTRONICS™ of Geneva, Switzerland draw 195 μA to 233 μA per MHzdepending on architecture.

In some embodiments, 20 FPS (frames per second) is achievable withreadily available microcontrollers operating at 1 MHz with oneinstruction execution per clock cycle, or 1 MIPS. For a typical CPUconsuming 300 μA per MIPS and operating directly from the batteryvoltage, this would consume about 20% of the power budget. In someembodiments, CPU speed is increased to increase processing bandwidth tosupport a higher frame rate, but power consumption would also riseproportionately.

In an experimental embodiment, the FREESCALE KINETIS K10 was used. ThisCPU is housed in a rather large package that isn't suitable forintegration into a production prosthetic, but it provides resources thatwere useful in the bench model.

In some embodiments, the Freescale KL02 CSP microprocessor is used asthe CPU. The device contains 32 KB Flash memory, 4 KB RAM, a 32 bit ARMcore, and a 12 bit (effective) multi-channel AID converter. The packageis just 2×2 mm and supports 18 input/output pins. The optical sensormultiplexor is built from 5 enables and 5 AID channels, permitting us tosample 25 different input signals. An optical array that uses 3-6-12sensor rings consumes a total of 21 inputs. An additional opticalchannel handles the ambient light sensor, leaving three channelsavailable for housekeeping functions such as battery management. Bysupporting 21 position sensors (instead of the 16 found in the earlierbench model) improved position detection and better utilization of theoptical beacon are both achieved.

2.6 Memory

Memory is cheap and small but does consume power. The amount of memorydepends on the configuration data and software instructions in variousembodiments. In some embodiments, the amount of memory is stronglyaffected by the storage of images associated with different pupildilations. The range of pupil dilations is approximately 2 to 6 mm. Thisequates to about 6 to 20 pixels. If a separate eye image for every 1pixel change in pupil diameter, in some embodiments, then 15 images arestored. There are several methods of storing the eye image in memory.

In one set of embodiments, an iris image on an oversize sclera field isstored so that as the image pans left-right and up-down, the off-screensclera image portion scrolls into view, as depicted in FIG. 9C. In someembodiments, the image size used for this image is twice the height andtwice the width of the display area, which is four times the displaysize. In some embodiments this is 3380*4=13,520 pixels. The memory sizeat 2 bytes per pixel is 27,040 bytes.

In another set of embodiments, the eye image wraps around as the eyepans left to right and blanks as the eye pans up and down. The imagesize for this case is the same as the display size, 3380 pixels. Thememory size is 6760 bytes.

In another set of embodiments, the sclera features are static and onlythe rectangular iris area is stored as an image, requiring 3380/2=1640pixels. The memory size is 3380 bytes.

In another set of embodiments, the images are folded along the verticaland horizontal axis centered on the pupil so that only one quarter ofthe image is stored, thus reducing the image and memory sizes in cases 1thru 4 to 25% of their unfolded size. The memory size for case 3 becomes845 bytes.

In another set of embodiments, a 2 color scheme is used with a 4-bitcolor depth; and, only one byte per pixel is stored and the memory sizefor case 4 becomes 423 bytes.

In various embodiments, computer cycles are traded for memory size. Thatis, the 4× folded image takes up a less storage space, but it requiresthe CPU to unfold the image while updating the display. In someembodiments, the onboard memory of the CPU chip, typically 128 kB isused for the combination of program and image storage. It is estimatedthat, with this much memory available in some embodiments, the imageconstruction algorithm supports 20 frames per second at 1 MIPScomputational rate.

2.7 Communication Module

In various embodiments, communication module 313 is used for deviceconfiguration and programming through optical or RF means. The opticalapproach suggests itself because an ambient light sensor is alreadyincluded in some embodiments. Thus in some embodiments, a second use ismade of this sensor as an optical data receiver, although it would notbe spectrally compatible with the Gas LEDs used in typical hand heldoptical programming devices (such as television remote controls). Insome embodiments, an optical transmitter is added for a secure(verifiable) communication loop. The optical transmitter might representa significant power sink.

In other embodiments, one or more of a number of radio frequencycommunication standards are used, which already target short rangecommunication, medical devices, and very low power consumption.Additional RF circuitry is included in these embodiments. The RF antennaitself should not be problem and in various embodiments is shared withone or more other components. For example, in some embodiments, theelectrodes inside the battery are driven as an antenna. Given theinherently low power consumption of these RF links and the intermittentneed for communication (only during setup) the power consumption shouldnot be an issue in these embodiments.

2.8 Housing Form Factor

FIG. 20 is a block diagram that illustrates example disposition, in avertical cross section, of components of an ocular prosthesis in ahousing 901 with a form factor suitable for insertion as an ocularprosthesis under an eyelid of a subject and anterior to an orbitalimplant, according to an embodiment. In a vertical cross section of thehousing 901 are shown the display 910 serving as display device 311; amicrocontroller and memory chip 2001 serving as processor 301; a battery2003 serving as power storage/supply 303 and induction coil 2005 servingas charge receiving device 305 and a power conversion module 2006 allserving as power source 302, an ambient light sensor and circuitry 2007serving as light sensor 307, a communications module 2013 andantenna/induction coil 2005 serving as communications module 313; andmotion sensor circuitry 2009, such as an array of 16 photodiodes andcircuitry, including part of microcontroller and memory 2001 serving asimplant detector 309. Also shown is glue logic and support circuitry2020 that helps connect the various components and control access tovarious functions, such as microcontroller 2001 and power from battery2003 and use of antenna/induction coil 2005.

In some embodiments, the microcontroller and other larger semiconductordevices are die level assembled to minimize the volume penalty of theelectronics packaging. While this is the most space efficientimplementation of the electronics, it presents other costs andcomplexities in handling, assembly methods and testing. Themicrocontroller investigation revealed newer types of “wafer scale”packaging as small as 1.7 mm×2.9 mm×0.6 mm for an 8-bit ST Semiconductormicrocontroller in a WLCS28 package. Since this is a standard packagedconfiguration, it has significant logistics and manufacturing benefitsover a bare die, and still with a small volume penalty. Thus, such waferscale packaging is used in some embodiments. Some embodiments use baredie components and assembly methods for some components but not others.

FIG. 20 illustrates a concept rendition for the ocular prosthesisdepicting representative functional block volume models encapsulated ina housing 901 made of a castable medium, such as acrylic resin. Table 1shows the volume demand by functional unit.

TABLE 1 Volume estimates by functional block. Component/ Thick-Functional Length Width ness Volume block (mm) (mm) (mm) (mm³) NotesBattery 19.0 10.8 2.4 492.5 Power 6.0 6.0 2.5 90.0 conversion Display28.0 13.0 0.1 31.8 Microcontroller 4.0 4.0 0.6 4.6 Ambient light 2.2 2.22.0 9.7 sensor Motion sensor 2.0 3.0 0.8 4.8 x 16 circuit Support 3.03.0 0.5 4.5 circuitry Total Volume 709.9 Estimated 2800.0 Largeprosthesis available 1800.0 Small prosthesis volumeAs evident in Table 1, the battery volume dominates the space available.Since the electrolyte in lithium polymer battery chemistry is entrainedin a flexible solid material (polymer), it has the unique property thatit can be curved or easily shaped into irregular forms. Thischaracteristic of these batteries is highly beneficial in gaining spacein some embodiments.

In some embodiments, the bill of materials (BOM) is dominated by thecost of the display device. Estimates for the other electroniccomponents (CPU, battery, power conversion circuits, position sensor,light sensor, etc.) total approximately $100 at the time of thiswriting. However, purchasing a custom display in very small quantities(compared to consumer displays such as cell phones) is relativelyexpensive. The initial cost for the display is on the order of $1,000for some embodiments at the time of this writing. It is expected thatthis cost will drop as flexible reflective display technology becomesmore commonplace.

Some embodiments are expected to involve somewhat exotic assemblymethods. The fabrication costs are highly dependent on manufacturingvolume. At an anticipated volume of 10,000 units annually, a fabricationcost at the time of this writing is expected to be in the range of $100to $200 per unit.

None of the characteristics of the components of the ocular prosthesispresent an obstacle to generating various embodiments, Thus, a varietyof embodiments are currently feasible, and individual components, suchas a display and implant detector have been thoroughly demonstrated.

2.9. Spatial Packaging Model

Packaging of the electronic circuitry, battery and display to fit withinthe allowed space in the prosthesis was addressed with a more detailedspatial packaging model, described here. Elements of the circuit designand component selection were described in previous sections. Anadvancement in circuit design has been to place a tiny amplifierdirectly adjacent to each optical sensor of an implant detector. Thisamplifier produces a more robust signal that should be able to reach ananalog to digital converter (ADC) in the microprocessor without furthersignal conditioning. A 25 element (5×5) signal multiplexer wasimplemented using a sleep mode of the amplifier (5 selection signals)and five ADC input channels on the central processing unit (CPU) chip.In order to test this concept under realistic conditions, a flexibleprinted circuit was built that is faithful to the dimensions of theoptical prosthetic. The sensor signals are somewhat fragile and can't betransmitted noise-free over long distances.

A solution to the optical sensor/multiplexor problem is predicated onmaking a very compact circuit to not suffer from the electrical noisethat would result from long circuit traces. One solution is to constructthe bulk of the circuit using flexible circuitry that is very close tothe eventual production implementation. A flexible circuit “spider”commits an arm to each optical sensor. The endpoint of the arm carries aphotodiode and its supporting amplifier. Outgoing signals from thecircuit down each arm include power and enable; the returned signalincludes a voltage representing the light input to the photodiode. Byplacing each optical sensor on its own arm of the spider, it is possibleto locate the sensor in the correct position within the cup thatrepresents the back surface of the prosthetic cover. Keeping everythingminiaturized improves signal quality. This approach has been implementedat first as a bench circuit to provide a realistic example of how theproduction circuit will behave.

A look at a planned flex circuit card is provided in FIG. 23A throughFIG. 23C. FIG. 23A and FIG. 23B are block diagrams that illustrateassembly of an example array of photodetectors for implant markerdetection for a spatial model of the ocular prosthesis, according to anembodiment. The array of photodetectors are assembled on a flex circuitcard 2310, depicted in a pre-folded state 2300 in FIG. 23A and foldedstate 2301 in FIG. 23B. The ring around a center opening 2311 fits thebase dimension of a prosthetic cover, described below. There are 21 armsextending from the ring which carry the elements 2320 that include theoptical sensors 2322 on a posterior face (in the folded state 2301) andsupport electronics 2324 on an anterior face (in the folded state 2301).Another arm carries the ambient light sensor 2328. When this flexcircuit gets folded up, as depicted in FIG. 23B all of these elementsfit into the space available in the prosthesis on a posterior sidefacing the orbital implant. Each “leaf’ carries an optical sensor 2322that lies on the back (posterior) side of the prosthesis. The sensors2322 sit on a spherical surface with about 24 mm diameter, so that thesensors 2322 can view an optical beacon implanted in the conjunctiva ofthe patient in front of the orbital implant. The folded aims bring thesensors quite close together for good coverage of the optical beacon.Excess loops 2303 evident in the test flex card are not included in thedeployed folded state by reducing appropriately the lengths of the armsof the flex card. The rectangle portion 2312 carries circuitry such asthe microprocessor, battery management circuit, communications andbeacon power source. These circuits are small enough to fit within theprosthesis, but they are packaged externally in a bench model in orderto facilitate testing and debugs.

FIG. 23C is a block diagram that illustrates a detail of an exampleanterior face of one photodetector array element 2320, according to anembodiment. This face is directed to the anterior of the ocularprosthesis when in the folded state 2310 and includes supportelectronics 2324, such as amplifier 2331 and other circuit components2333, such as resisters and capacitors. The amplifier 2324 sits directlybehind the optical sensor. These are “0201” surface mount components,just 0.020″ long by 0.010″ square. Power, ground, input and outputsignals travel down the arms to the “ring” and then around to themicroprocessor. In some embodiments, the signals are buried betweenpower and ground planes for good noise performance.

FIG. 24A through FIG. 24C are block diagrams that illustrate an examplespatial model of an ocular prosthesis, according to an embodiment. Wheneverything is assembled into the prosthesis 2400, the view from the backlooks like that depicted in FIG. 24A. This gives a better picture of howthe sensors are located over the orbital implant in folded state 2301.Note that the latest sensor configuration has no “north pole” sensor.The old configuration was 1-5-10 sensors in three rings. The newconfiguration is 3-6-12 sensors to provide good coverage while keepingthe sensors as close as possible to the beacon (for better spaceutilization). The flex circuit board in folded state 2301 sits inside acover or housing 2410, that is transparent in at least a portionanterior to the a display device. Apparent in FIG. 24A, beyond the flexcircuit in folded state 2301 is a shaped battery 2420.

FIG. 24B is a cross-sectional view of the prosthesis 2400 from left toright. The flex circuit, in folded state 2301, shows as a thin objectnear the bottom of the figure, with the ambient light sensor 2328extending outside the sphere of the other sensors. The 21 opticalposition sensors and their flexible arms are hidden in this view. In theproduction version of the circuitry, the “saddlebag” areas (lower leftand right) of housing 2410 house the remaining circuits such as CPU,battery management, and communications. This region of the prosthesis ismostly inaccessible to other design elements, so the space isessentially “free.” There is actually more space in the saddlebags thanrequired by the planned circuitry. The central object in FIG. 24B is thebattery 2420 and the dark object is the curved display screen 2430.These two elements have proven to be the most difficult to packageinside the prosthesis. The goal in this design iteration was to utilizea “single curved” display. This is conceived as being a flat displaythat is built on a flexible substrate. The substrate can be bent ineither axis (chosen here to be the long horizontal direction) but not inboth axes at once. In FIG. 24B it looks like the display fits easilyinside the envelope of the prosthesis, but in truth it's a very tightfit in the other dimensions. The housing 2410 includes a transparentportion 2411 so that the screen 2430 is visible at the anterior of theprosthesis 2400. In some embodiments, the entire housing 2410 is made oftransparent material.

FIG. 24C is a cutaway view of the prosthesis from top to bottom withoutthe housing. The flex circuit, in folded state 2301, shows as the lowersphere portion. The cutaway is taken through the center of theprosthesis. The display screen 2430 looks flat here because the sliceaxis is in the non-curved vertical direction. Note how the displayscreen 2430 sits directly on top of the central optical sensors and thebattery 2420.

FIG. 24D is a front (anterior) view of prosthesis 2400. The housing 2410is transparent enough to reveal the screen 2430, the battery 2430 behindthe screen, the ambient light sensor 2328 and some other portions of theflex circuit card in folded state 2301. The battery is depicted inseveral shades of gray because the battery changes surface angles to fitwithin the housing 2410. Note that the corners of the display screen2430 are rounded to keep the screen 2430 from penetrating the housing2410 of the prosthesis 2400. This model of the display screen 2430 is 25mm×14.5 mm×1.5 mm. It is anticipated that this shape provides adequatecoverage for all sensible pointing angles of the eye. It appears thatthe clipped corners do not harm the appearance, because these areas willnormally be covered by the patient's eyelids.

FIG. 25A and FIG. 25B are block diagrams that illustrate an exampleshaped battery component 2420 of the spatial model of an ocularprosthesis 2400, according to an embodiment. With the display screen2410 taking up all of the “good” volume of the prosthesis, the batteryneeds to fit in the space between the screen and the flex circuit boardwith photosensors in folded state 2301, depicted din FIG. 25A inperspective view. The bottom of the battery 2420 is shaped to wraparound the optical sensors; and, the central area is thinned to makeroom for the display. The thinned central portion is shown in thecutaway perspective view in FIG. 25B. This intricate shape suggestsusing a printable battery technology. A solution was not found toposition one or more standard batteries in the prosthesis, always withthe goal of yielding at least 80 mW-hrs of capacity (25 mA-hrs at 3.3V).The good news is that a rechargeable lithium ion battery of 80 mW-hrscapacity requires a volume of just 470 mm³. By comparison, the printablebattery shown has a volume of 1800 mm³. This fact provides a choice inbattery solutions. A fully printable battery could utilize the full 1800mm³ volume. This is about 4× the volume required by lithium ion, so theprintable battery could have a much less space efficient chemistry, suchas one of the zinc formulations. Another choice is a lithium polymerbattery with a non-printable, but custom shape. Using the lithiumchemistry, one could simplify the shape by giving up a lot of volume,especially in the interior of the battery space.

3. PROCESSOR HARDWARE OVERVIEW

FIG. 21 is a block diagram that illustrates a computer system 2100 uponwhich an embodiment of the invention may be implemented. Computer system2100 includes a communication mechanism such as a bus 2110 for passinginformation between other internal and external components of thecomputer system 2100. Information is represented as physical signals ofa measurable phenomenon, typically electric voltages, but including, inother embodiments, such phenomena as magnetic, electromagnetic,pressure, chemical, molecular atomic and quantum interactions. Forexample, north and south magnetic fields, or a zero and non-zeroelectric voltage, represent two states (0, 1) of a binary digit (bit).Other phenomena can represent digits of a higher base. A superpositionof multiple simultaneous quantum states before measurement represents aquantum bit (qubit). A sequence of one or more digits constitutesdigital data that is used to represent a number or code for a character.In some embodiments, information called analog data is represented by anear continuum of measurable values within a particular range. Computersystem 2100, or a portion thereof, constitutes a means for performingone or more steps of one or more methods described herein.

A sequence of binary digits constitutes digital data that is used torepresent a number or code for a character. A bus 2110 includes manyparallel conductors of information so that information is transferredquickly among devices coupled to the bus 2110. One or more processors2102 for processing information are coupled with the bus 2110. Aprocessor 2102 performs a set of operations on information. The set ofoperations include bringing information in from the bus 2110 and placinginformation on the bus 2110. The set of operations also typicallyinclude comparing two or more units of information, shifting positionsof units of information, and combining two or more units of information,such as by addition or multiplication. A sequence of operations to beexecuted by the processor 2102 constitutes computer instructions.

Computer system 2100 also includes a memory 2104 coupled to bus 2110.The memory 2104, such as a random access memory (RAM) or other dynamicstorage device, stores information including computer instructions.Dynamic memory allows information stored therein to be changed by thecomputer system 2100. RAM allows a unit of information stored at alocation called a memory address to be stored and retrievedindependently of information at neighboring addresses. The memory 2104is also used by the processor 2102 to store temporary values duringexecution of computer instructions. The computer system 2100 alsoincludes a read only memory (ROM) 2106 or other static storage devicecoupled to the bus 2110 for storing static information, includinginstructions, that is not changed by the computer system 2100. Alsocoupled to bus 2110 is a non-volatile (persistent) storage device 2108,such as a magnetic disk or optical disk, for storing information,including instructions, that persists even when the computer system 2100is turned off or otherwise loses power.

Information, including instructions, is provided to the bus 2110 for useby the processor from an external input device 2112, such as a keyboardcontaining alphanumeric keys operated by a human user, or a sensor. Asensor detects conditions in its vicinity and transforms thosedetections into signals compatible with the signals used to representinformation in computer system 2100. Other external devices coupled tobus 2110, used primarily for interacting with humans, include anelectronic display device 2114, such as a cathode ray tube (CRT) or aliquid crystal display (LCD), for presenting images, and a pointingdevice 2116, such as a mouse or a trackball or cursor direction keys,for controlling a position of a small cursor image presented on thedisplay 2114 and issuing commands associated with graphical elementspresented on the display 2114.

In the illustrated embodiment, special purpose hardware, such as anapplication specific integrated circuit (IC) 2120, is coupled to bus2110. The special purpose hardware is configured to perform operationsnot performed by processor 2102 quickly enough for special purposes.Examples of application specific ICs include graphics accelerator cardsfor generating images for display 2114, cryptographic boards forencrypting and decrypting messages sent over a network, speechrecognition, and interfaces to special external devices, such as roboticarms and medical scanning equipment that repeatedly perform some complexsequence of operations that are more efficiently implemented inhardware.

Computer system 2100 also includes one or more instances of acommunications interface 2170 coupled to bus 2110. Communicationinterface 2170 provides a two-way communication coupling to a variety ofexternal devices that operate with their own processors, such asprinters, scanners and external disks. In general the coupling is with anetwork link 2178 that is connected to a local network 2180 to which avariety of external devices with their own processors are connected. Forexample, communication interface 2170 may be a parallel port or a serialport or a universal serial bus (USB) port on a personal computer. Insome embodiments, communications interface 2170 is an integratedservices digital network (ISDN) card or a digital subscriber line (DSL)card or a telephone modem that provides an information communicationconnection to a corresponding type of telephone line. In someembodiments, a communication interface 2170 is a cable modem thatconverts signals on bus 2110 into signals for a communication connectionover a coaxial cable or into optical signals for a communicationconnection over a fiber optic cable. As another example, communicationsinterface 2170 may be a local area network (LAN) card to provide a datacommunication connection to a compatible LAN, such as Ethernet. Wirelesslinks may also be implemented. Carrier waves, such as acoustic waves andelectromagnetic waves, including radio, optical and infrared wavestravel through space without wires or cables. Signals include man-madevariations in amplitude, frequency, phase, polarization or otherphysical properties of carrier waves. For wireless links, thecommunications interface 2170 sends and receives electrical, acoustic orelectromagnetic signals, including infrared and optical signals, thatcarry information streams, such as digital data.

The term computer-readable medium is used herein to refer to any mediumthat participates in providing information to processor 2102, includinginstructions for execution. Such a medium may take many forms,including, but not limited to, non-volatile media, volatile media andtransmission media. Non-volatile media include, for example, optical ormagnetic disks, such as storage device 2108. Volatile media include, forexample, dynamic memory 2104. Transmission media include, for example,coaxial cables, copper wire, fiber optic cables, and waves that travelthrough space without wires or cables, such as acoustic waves andelectromagnetic waves, including radio, optical and infrared waves. Theterm computer-readable storage medium is used herein to refer to anymedium that participates in providing information to processor 2102,except for transmission media.

Common forms of computer-readable media include, for example, a floppydisk, a flexible disk, a hard disk, a magnetic tape, or any othermagnetic medium, a compact disk ROM (CD-ROM), a digital video disk (DVD)or any other optical medium, punch cards, paper tape, or any otherphysical medium with patterns of holes, a RAM, a programmable ROM(PROM), an erasable PROM (EPROM), a FLASH-EPROM, or any other memorychip or cartridge, a carrier wave, or any other medium from which acomputer can read. The term non-transitory computer-readable storagemedium is used herein to refer to any medium that participates inproviding information to processor 2102, except for carrier waves andother signals.

Logic encoded in one or more tangible media includes one or both ofprocessor instructions on a computer-readable storage media and specialpurpose hardware, such as ASIC *2120.

Network link 2178 typically provides information communication throughone or more networks to other devices that use or process theinformation. For example, network link 2178 may provide a connectionthrough local network 2180 to a host computer 2182 or to equipment 2184operated by an Internet Service Provider (ISP). ISP equipment 2184 inturn provides data communication services through the public, world-widepacket-switching communication network of networks now commonly referredto as the Internet 2190. A computer called a server 2192 connected tothe Internet provides a service in response to information received overthe Internet. For example, server 2192 provides information representingvideo data for presentation at display 2114.

The invention is related to the use of computer system 2100 forimplementing the techniques described herein. According to oneembodiment of the invention, those techniques are performed by computersystem 2100 in response to processor 2102 executing one or moresequences of one or more instructions contained in memory 2104. Suchinstructions, also called software and program code, may be read intomemory 2104 from another computer-readable medium such as storage device2108. Execution of the sequences of instructions contained in memory2104 causes processor 2102 to perform the method steps described herein.In alternative embodiments, hardware, such as application specificintegrated circuit 2120, may be used in place of or in combination withsoftware and a general purpose processor to implement the invention.Thus, embodiments of the invention are not limited to any specificcombination of specific hardware and software with general purposehardware.

The signals transmitted over network link 2178 and other networksthrough communications interface 2170, carry information to and fromcomputer system 2100. Computer system 2100 can send and receiveinformation, including program code, through the networks 2180, 2190among others, through network link 2178 and communications interface2170. In an example using the Internet 2190, a server 2192 transmitsprogram code for a particular application, requested by a message sentfrom computer 2100, through Internet 2190, ISP equipment 2184, localnetwork 2180 and communications interface 2170. The received code may beexecuted by processor 2102 as it is received, or may be stored instorage device 2108 or other non-volatile storage for later execution,or both. In this manner, computer system 2100 may obtain applicationprogram code in the form of a signal on a carrier wave.

Various forms of computer readable media may be involved in carrying oneor more sequence of instructions or data or both to processor 2102 forexecution. For example, instructions and data may initially be carriedon a magnetic disk of a remote computer such as host 2182. The remotecomputer loads the instructions and data into its dynamic memory andsends the instructions and data over a telephone line using a modem. Amodem local to the computer system 2100 receives the instructions anddata on a telephone line and uses an infrared transmitter to convert theinstructions and data to a signal on an infrared carrier wave serving asthe network link 2178. An infrared detector serving as communicationsinterface 2170 receives the instructions and data carried in theinfrared signal and places information representing the instructions anddata onto bus 2110. Bus 2110 carries the information to memory 2104 fromwhich processor 2102 retrieves and executes the instructions using someof the data sent with the instructions. The instructions and datareceived in memory 2104 may optionally be stored on storage device 2108,either before or after execution by the processor 2102.

FIG. 22 illustrates a chip set 2200 upon which an embodiment of theinvention may be implemented. Chip set 2200 is programmed to perform oneor more steps of a method described herein and includes, for instance,the processor and memory components described with respect to FIG. 21incorporated in one or more physical packages (e.g., chips). By way ofexample, a physical package includes an arrangement of one or morematerials, components, and/or wires on a structural assembly (e.g., abaseboard) to provide one or more characteristics such as physicalstrength, conservation of size, and/or limitation of electricalinteraction. It is contemplated that in certain embodiments the chip setcan be implemented in a single chip. Chip set 2200, or a portionthereof, constitutes a means for performing one or more steps of amethod described herein.

In one embodiment, the chip set 2200 includes a communication mechanismsuch as a bus 2201 for passing information among the components of thechip set 2200. A processor 2203 has connectivity to the bus 2201 toexecute instructions and process information stored in, for example, amemory 2205. The processor 2203 may include one or more processing coreswith each core configured to perform independently. A multi-coreprocessor enables multiprocessing within a single physical package.Examples of a multi-core processor include two, four, eight, or greaternumbers of processing cores. Alternatively or in addition, the processor2203 may include one or more microprocessors configured in tandem viathe bus 2201 to enable independent execution of instructions,pipelining, and multithreading. The processor 2203 may also beaccompanied with one or more specialized components to perform certainprocessing functions and tasks such as one or more digital signalprocessors (DSP) 2207, or one or more application-specific integratedcircuits (ASIC) 2209. A DSP 2207 typically is configured to processreal-world signals (e.g., sound) in real time independently of theprocessor 2203. Similarly, an ASIC 2209 can be configured to performedspecialized functions not easily performed by a general purposedprocessor. Other specialized components to aid in performing theinventive functions described herein include one or more fieldprogrammable gate arrays (FPGA) (not shown), one or more controllers(not shown), or one or more other special-purpose computer chips.

The processor 2203 and accompanying components have connectivity to thememory 2205 via the bus 2201. The memory 2205 includes both dynamicmemory (e.g., RAM, magnetic disk, writable optical disk, etc.) andstatic memory (e.g., ROM, CD-ROM, etc.) for storing executableinstructions that when executed perform one or more steps of a methoddescribed herein. The memory 2205 also stores the data associated withor generated by the execution of one or more steps of the methodsdescribed herein.

4. ALTERNATIVES AND MODIFICATIONS

In the foregoing specification, the invention has been described withreference to specific embodiments thereof. It will, however, be evidentthat various modifications and changes may be made thereto withoutdeparting from the broader spirit and scope of the invention. Thespecification and drawings are, accordingly, to be regarded in anillustrative rather than a restrictive sense. Throughout thisspecification and the claims, unless the context requires otherwise, theword “comprise” and its variations, such as “comprises” and“comprising,” will be understood to imply the inclusion of a stateditem, element or step or group of items, elements or steps but not theexclusion of any other item, element or step or group of items. elementsor steps. Furthermore, the indefinite article “a” or “an” is meant toindicate one or more of the item, element or step modified by thearticle.

What is claimed is:
 1. An ocular prosthesis comprising a display devicevisible at an anterior portion of the ocular prosthesis, wherein thedisplay device is configured to present a changeable image thatrepresents a natural appearance and movement for a visible portion of aneyeball of a subject.
 2. An ocular prosthesis as recited in claim 1,further comprising: a housing having a form factor shaped to fit underan eyelid of the subject and in front of an orbital implant disposed inan eye socket of the subject, wherein an anterior portion of the formfactor is curved similar to an anterior portion of a natural eyeball forthe subject; wherein the display device is disposed within the housingand visible at an anterior portion of the housing; an implant detectordisposed within the housing and configured to detect angular orientationof the orbital implant relative to the subject when the housing isinserted under the eyelid of the subject and anterior to the orbitalimplant; a processor disposed within the housing and configured todetermine, at least in part, the natural appearance for the visibleportion of the eyeball of the subject based, at least in part, on theangular orientation of the orbital implant, and render, at least inpart, an image for presentation on the display as the changeable imagebased on the natural appearance for the visible portion of the eyeballof the subject; and a power source disposed within the housing andconfigured to provide power for the display device, the implant detectorand the processor.
 3. An ocular prosthesis as recited in claim 2,further comprising a computer-readable memory disposed within thehousing and configured to store data that indicates a color image of aniris for the subject, wherein to determine the natural appearance forthe visible portion of the eyeball of the subject further comprises todetermine the natural appearance based, at least in part, on the imageof the iris.
 4. An ocular prosthesis as recited in claim 2, furthercomprising a light sensor disposed within the housing and configured todetect ambient light level on an anterior portion of the housing,wherein to determine the natural appearance for the visible portion ofthe eyeball of the subject further comprises to determine a size of apupil based, at least in part, on the ambient light level.
 5. An ocularprosthesis as recited in claim 2, further comprising a communicationmodule configured to receive configuration data for the processor.
 6. Anocular prosthesis as recited in claim 2, wherein the power sourcefurther comprises an induction coil configured to produce an electriccurrent in response to external electromagnetic radiation.
 7. An ocularprosthesis as recited in claim 6, wherein the induction coil is furtherconfigured as an antenna for a communication module configured toreceive configuration data for the processor.
 8. An ocular prosthesis asrecited in claim 6, wherein the power source further comprises arechargeable battery configured to be charged by the electric currentproduced in the induction coil.
 9. An ocular prosthesis as recited inclaim 2, wherein the display device is an electronic reflective displaydevice with an display area of about 13 millimeters vertically and about25 millimeters horizontally.
 10. An ocular prosthesis as recited inclaim 2, wherein the display device is an electronic reflective displaydevice with a resolution of about 81 picture elements per inch and arefresh rate of about 18 frames per second.
 11. An ocular prosthesis asrecited in claim 2, wherein the display device is a flexible electronicreflective display device curved in at least a horizontal plane similarto the anterior portion of the housing.
 12. An ocular prosthesis asrecited in claim 2, wherein the display device is shaped as a rectanglewith rounded corners.
 13. An ocular prosthesis as recited in claim 2,wherein the implant detector is further configured to detect an implantmarker configured to move with the orbital implant.
 14. An ocularprosthesis as recited in claim 13, wherein. the implant marker is amagnet; and the implant detector is configured to detect a Hall effectwhen the implant marker moves.
 15. An ocular prosthesis as recited inclaim 13, wherein. the implant marker is a non-magnetic metal foil, theimplant detector further comprises a plurality of non-magnetic metalfoils configured to form a variable capacitor; and the implant detectoris configured to detect a change in capacitance when the implant markermoves.
 16. An ocular prosthesis as recited in claim 13, wherein. theimplant marker is a light source, the implant detector further comprisesa plurality of light detectors; and the implant detector is configuredto determine changes in light intensities detected from the light sourcein at least three of the plurality of light detectors.
 17. An ocularprosthesis as recited in claim 16, wherein. a first light detector ofthe plurality of light detectors is disposed near a center of aposterior side of the housing, a first subset of the plurality of lightdetectors different from the first light detector is disposed near anouter edge of the posterior side of the housing; and a second subset ofthe plurality of light detectors different from the first subset and thefirst light detector is disposed between the center and the outer edgeof the posterior side of the housing.
 18. An ocular prosthesis asrecited in claim 16, wherein, the implant marker comprises fluorescentmaterial in a vessel configured to be attached to a subject'sconjunctiva adjacent to the orbital implant; and the implant detectorfurther comprises a light emitting diode to excite the fluorescentmaterial.
 19. An ocular prosthesis as recited in claim 16, wherein, theimplant marker is light emitting diode powered by a receiving antennadisposed inside a vessel configured to be attached to a subject'sconjunctiva adjacent to the orbital implant; the ocular prosthesisfurther comprises a transmitting antenna disposed within the housing;and the implant detector is further configured to power the lightemitting diode by sending a time varying current through thetransmitting antenna to be received at the receiving antenna.
 20. Anocular prosthesis as recited in claim 16, wherein the plurality of lightdetectors comprises a plurality of photodiodes; and the implant detectorfurther comprises: a plurality of dual matched preamps, each pair ofdual matched preamps connected to one photodiode of the plurality ofphotodiodes; a plurality of differential output amplifiers, eachdifferential output amplifier connected to one pair of dual matchedpreamps of the plurality of dual matched preamps; and a multiplexerconnected to the plurality of differential output amplifiers.
 21. Anocular prosthesis as recited in claim 16, wherein the plurality of lightdetectors comprises a plurality of photodiodes; and the implant detectorfurther comprises a circuit configured to bias each photodiode at zerobias voltage.
 22. An ocular prosthesis as recited in claim 13, wherein.the implant marker is a non-magnetic conductor, the implant detectorfurther comprises a plurality of inductance sensors; and the implantdetector is configured to detect a change in inductance when the implantmarker moves.
 23. An ocular prosthetic system comprising: a implantmarker configured to move with an orbital implant disposed in an eyesocket of a subject; and an ocular prosthesis comprising a housinghaving a form factor shaped to fit under an eyelid of the subject and infront of the orbital implant, wherein an anterior portion of the formfactor is curved similar to an anterior portion of a natural eyeball forthe subject; a display device disposed within the housing and visible atan anterior portion of the housing; an implant detector disposed withinthe housing and configured to detect a position of the implant markerwhen the housing is inserted under the eyelid of the subject andanterior to the orbital implant; and a processor disposed within thehousing and configured to determine, at least in part, a naturalappearance for a visible portion of the eyeball of the subject based, atleast in part, on the position of the implant marker, and render, atleast in part, an image for presentation on the display device based onthe natural appearance for the visible portion of the eyeball of thesubject.
 24. A system as recited in claim 23, further comprising anexternal wearable device configured to provide power to the ocularprosthesis.
 25. A system as recited in claim 23, further comprising anexternal wearable device configured to determine, at least in part, thenatural appearance for the visible portion of the eyeball of thesubject.
 26. A method comprising: determining a change in orientation ofan orbital implant in a subject; determining an update to a naturalappearance for a visible portion of an eyeball for the subject based onthe change in orientation of the orbital implant; and rendering anupdate to an image of the natural appearance for a display devicedisposed in an ocular prosthesis configured to be dinserted in thesubject anterior to the orbital implant.
 27. A computer-readable mediumcarrying one or more sequences of instructions, wherein execution of theone or more sequences of instructions by one or more processors causesan apparatus to perform the steps of: determining a change inorientation of an orbital implant in a subject; determining an update toa natural appearance for a visible portion of an eyeball for the subjectbased on the change in orientation of the orbital implant; and renderingan update to an image of the natural appearance for a display devicedisposed in an ocular prosthesis configured to be inserted in thesubject anterior to the orbital implant.
 28. An apparatus comprising: atleast one processor; and at least one memory including one or moresequences of instructions, the at least one memory and the one or moresequences of instructions configured to, with the at least oneprocessor, cause the apparatus to perform at least the following,determining a change in orientation of an orbital implant in a subject;determining an update to a natural appearance for a visible portion ofan eyeball for the subject based on the change in orientation of theorbital implant; and rendering an update to an image of the naturalappearance for a display device disposed in an ocular prosthesisconfigured to be inserted in the subject anterior to the orbitalimplant.
 29. An apparatus comprising: a housing comprising a broadportion configured to be attached to an orbital implant or conjunctivatissue adjacent to the orbital implant; and a detectable device disposedin the housing adjacent to the broad portion, wherein the detectabledevice is configured to be detected remotely.
 30. An apparatus asrecited in claim 29, wherein the broad portion further comprises afenestration configured to allow conjunctiva tissue fixation to preventmigration of the apparatus relative to the orbital implant.
 31. Anapparatus as recited in claim 29, wherein the housing comprisesbilateral broad portions disposed on opposite sides of the detectabledevice.
 32. An apparatus as recited in claim 29, wherein the housing isabout 1 millimeter thick or less and about 15 millimeters long or lessand about 2 millimeters wide or less.